This tendency to climb is not related to the wing section or the incidence angles. If you alter the wing or stabilizer incidence without doing anything else you will merely change the static trim for the model. In flight you'll end up compensating for that by altering the elevator trim until you're right back where you started.

So what is making the model climb? It's the CG position and the resulting trim the model requires to fly level in cruise. If you move the CG back you'll need less decalage (the angle between the wing and stabilizer). And less decalage means a weaker tendency for the model to want to climb with a change in airspeed.

First off a airplane that wants to climb when speed is added is entirely natural and desireable in all but fancy aerobatic stuff. However what happens when the tendency is too strong is we end up fighting the model all the time.

Now obviously you don't want the model to react like a totally dead neutral "point and shoot" 3D aerobatic model. A Porter just isn't that sort of flyer. So a compromise needs to be found. You want to move the CG back in small amounts that are equal to about 1% of the chord until you find that it flies more to your liking. Obviously moving the CG back will require some down trim be added to where the elevator is at the moment. Test this with the engine at a steady moderate to low power setting by diving the model and then letting go of the stick to see how strongly it wants to lift the nose as the speed builds. Also you can test this by seeing how much down stick you need to hold the dive. When it seems to be flying with a slight but easily managed tendency to lift the nose in high speed dives and maneuvers NOW play with adding a little downthrust. However don't try to add enough downthrust to totally kill any tendency to climb. Climbing with added power is totally natural and desireable for this type of model. You just want it to get to where it doesn't nose up so strongly that it's unmanagable. By balancing the trimming between finding the best CG position and adding a little downthrust you'll end up with a model that flies well at cruise, goes into a nicer glide rather than a strong dive when the throttle is cut and climbs in a calm and natural looking manner when full throttle is used. If you go too far with moving the CG back you'll find that the model will get to where it doesn't want to pull itself out of a dive on it's own. It won't be UNstable but you'll find that you need to be on it more for watching out for pitch changes due to your flying and from encountering turbulence. What's happened is that you're setting it too close to the neutral point. That's fine for aerobatic models but not nice for a scale'ish style of flying unless you're a hot dogging aerobatic type and don't mind the feel of this and having to be on top of your model all the time. For most casual sport flyers though a moderate setting where the model still has a postive tendency to lift the nose in a dive but not do so TOO strongly is the best setting.

So why not just leave the CG where it is and add some downthrust? Because of the transition to an idle glide and how the model will behave when you go into a dive. If you don't optimize the CG position FIRST there will always be a strong tendency to nose over into a rather steep and fast glide when you cut the throttle. Also the downthrust only holds the nose down when you're using the engine for speed. If you dive the model out of a maneuver or a scale like steep spiral dive there will still be a super strong tendency to want to nose up strongly from the added airspeed. It'll have you complaining that the model wants to balloon all the time when you least expect it and that the airfoil is to blame because EVERYONE knows that flat bottom airfoils balloon, right? Nonsense, ANY airfoil will balloon from a high speed if the model trim is set up with a strongly forward CG location. So don't get sucked into that old wive's tale. Just because some is good this isn't a case where "too much is just right".

So how do you get the model to fly fast and level? There's this little control on our transmitters called an elevator trim. Learn to use it as a main flight control if you want to fly fast for a while. Then when you want to slow down use it again to add a bit of up trim. Real pilots do this and it soon becomes entirely natural. When I fly sailplanes the elevator trim is my "throttle" and I use the trim lever almost as much as I use the two sticks. If you just want to fly fast for a few seconds then learn to just ease the stick forward to hold the nose down when flying fast then ease off the pressure as the model slows down.

So to summarize. CG too far forward- strong tendency to lift nose during a dive or when throttle is applied and drop the nose strongly when speed is lost or throttle is cut. CG set just right- model still retains positive pitching stability but tendency to drop and lift the nose with speed changes is moderate and manageable with no surprises when something different is done. CG too far back- model is not quite pitch stable in all cases but has almost no tendency to climb or drop the nose with speed change but pilot must be on top of the model all the time. A "point and shoot" setting. Downthrust can help but it is a bandaid that can also cover up a bad trim setup.

Now in the end you're likely going to find that your elevator trim is quite strongly down. This will be the result of the rearward CG. Likely the elevator response will also sharpen up. If you don't like the quicker response then by all means reduce the amount of throw. As for the down angle just live with it. If it REALLY bugs you then measure the angle of the line between the leading and trailing edge of the stabilizer and elevator and slice into the model to move the stabilizer down to this new line. The model will then fly at your new trim with the elevator in line with the stabilizer. The ONLY advantage to this change will be how it looks on the ground. The model won't care when it's flying because the trim is set in concert with the CG position.