I dont understand this kind of concernes. I play mostly with 3rd party models, as Mig-21, Gripen, Rafale, VNAO F-18E or F-15E( this one is low poly thou) and i don't see any significant drop of performance by my computer, and i gotta say i use a laptop!
More trouble i get with fog or heavy clouds, so i don't see a reason for concerns with plane models high polycount. In fact i wish Tomcatz could make smoother models of his planes, especially F-15E, but i know its against his philosophy of making as much accurate model with as low polycount as possible.
My 2 cents :)