highroller,

Ivan is right - the scale speed is easier to achieve with light model and there is less power necessary in such case, but there is always a dark side too: when flying in a real world you mostly fly with wind - lighter or stronger - but you have to handle it. With models with wing loading like Ivan's I wish you good luck!!! Flying IS possible, but not really relaxing, and definitely it looks not very scale when light plane is shaked desperately with the winds.

And with the engines for my Kyosho - I had problems with first takeoffs (first attempts failed and we returned home to make some modifications), but soon it appeared, that it wasn't due to the power. Now after couple of flights I see, that .10 also would do.
The only advantage of larger engines is, that You can put larger, more scale looking props, and You can fly with half power, lower rpm-s which again looks, and after all sounds more scale.