The stock RC carbs are very restricitve, but gives you an idle down to 25000rpm for those who are into that. The MVVS .15 carb is direct drop in though, and will give you about 1500rpm extra, i.e. close to your home made venturi.

Here are some numbers with the muffler on:

Stock carb, APC 8x4 prop, 10% nitro: 14400rpm

MVVS carb, APC 8x4 prop, 10% nitro: 15800rpm

With the MVVS carb the performance pretty hard to match by any other .15 engine, especially if you consider the low overall weight of the engine.