Yes there is some tolerance, dictated by the design of the system. The less radically timed systems and muffled pipes tend to have a broader powerband - in this case referring to the boosted rpm range. It's a curve like any hp curve, with an upslope as you approach boosted conditions and peaking at highest power level, then dropping off again. The sweet area is wider and lower on some systems, narrower and taller on others (hence the term "peakier"). On a sport/pattern engine with a typical muffled tuned pipe system setup you will not see the hyperactive jumpiness you would except with a more radical setup like in F2A and other small engine CL speed stuff, the extreme examples, or open piped DF engines. These higher timed engines coupled with big fat narrow range open pipes have greater boost levels and higher potential peak horsepower, but in a more narrow operating range. So ultimately the boost level and manners of the system that you use are dictated by needs/wants. The old adage "you don't get something for nothing" always seems to surface. For RC speed flying where you care little about the 3/4 throttle settings, but need "FAST, some sort of cruise while I calm down, idle, stop" you can put up with more peakiness. For sport flying where you want some boost but want some tractability to be retained at mid throttle settings, a muffled tuned pipe system with the pipe not set on the short side is probably ideal. And you can see why as the system's state of tune gets higher and higher, carbs get more pointless/useless.

Unloading - think of how a wing works as you increase the angle of attack. Now think of the rotating wing called a prop - as the airspeed increases, the angle of attack of the prop blades is reduced (relative wind), less energy is being wasted as drag/turbulence and the efficiency of the propellor system increases. Fine pitch props reach pitch speed - the speed at which further increase results in a reduction of thrust - at lower airspeed. They also work more efficiently at low to zero airspeed due to the lower aqngle of attack, hence the much higher "static" thrust. Higher pitch props, conversely, bog the engine down on the ground and at low airspeed with the high angle of attack of the blades and resultant blade drag, so the engine is pulled off tune more and more as pitch goes up. As you can imagine there is a sweet spot in terms of airspeed for any prop, as well as for any engine/tuned exhaust system - your job is to home in on both those spots simultaneously.

Back to old tired car analogies, in terms of prop pitch, think of your engine as peaking at 5,000 on the tach, and imagine launching from the line in 1st, 2nd, 3rd gear respectively and how you would have to manage the clutch (prop slippage - turbulence, heat) to accomplish that, and the resultant performance as you pick up speed and approach 5k. Not a perfect analogy, but it's in the right direction.

In terms of rpm tolerance, the tuned muffler systems - Jett, Nelson et al - are very good examples of less ultimate boost (but pretty decent nonetheless), but broader powerband.

On your Magnum, sounds like you need to trim the header a bit (you've beem muttering about that haven't you?) or increase prop pitch a bit to reach top speed potential. In which case you'll have to launch a little more rich and toss harder. Or enjoy it where it is with lots of boost at launch and a little less top end. Perfect example of the decision making process with these things.

MJD