RE: Looking for something Faster!
There are many answers to that question.... but lets keep this very simple.
Your requirements are grass field, landing gear, no hand launch -- and you obviously want a smooth flying plane when you are done.
First, start off with a Jett 60LX engine.
(as noted, there are some "retired" 428 racing engines you might want to look in to as well if a throttle is not a requirement...)
Next, buy and build a GOOD Q-500 airframe. Does not have to be an all composite airframe ... but it could be.
(no, I do not include an ARF viper or predator II in that defined "good" category).
Bolt engine to plane.
Use a bubble-jett tank.
Bolt on a 8.8 x 8.75 prop
Standard 15% sport fuel
Effortless 150 mph. (probably closer to 160).
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Good wood kits out there. Look up Danny Kane's Hurrikane, Dave Normans Seeker, Lewis Schwab's PaceMaker3, and even older kits on ebay like a Doddger will suit the bill.
Matney Models Mad Dog and new Mad Dog 2 are great glass-foam basic kits.
Any above are designed for the flight loads and performance you are looking for. Build per the plans and instructions.
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If you want to go that fast with less engine.....
Again... build a good Q-500 airframe.
Build the wing as usual, but then clip each wing panel 4". That drops the span to about 42-44".
To that resulting airframe add anything from a TT46pro and jett-stream muffler combination --- on up in power.
There are indeed some deals to be had out in the market place for used Q-500 engines too. Dave's cautions are VERY valid. You could buy yourself a paperweight.
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Reason I said "GOOD" airframe ---- the Viper and Predator are nice kits ---- both fly great. I have flown both in 424 sport pylon configuration.
But neither is built properly 100% out of the box for the loads of a full blown 428 Q-500 engine, or the Jett 60LX engine. Just setting in some reality here folks - and trying to avoid problems others have experienced. So this may be more for the benifit of others who read the thread later, and not necessarily for the original poster...
If you are willing to do (and have the skills to do) some model building and improvements, yes, either of these can be made suitable. But consider this ... by the time you spend 10 hours or a few evenings modifying an ARF, you could have built one of the better kits - had the wing sheeted. Yes, they build quickly. And then you would be at the same point where you were going to start installing a radio and engine.