Please don't crucify me over this, but searching for 4 * on this board doesn't work too well because the words need to be at least 2 chars....

I'm looking to get a second plane for my son after he solos with his PT-40. Read a lot of the posts here and many agree that the Sig 4*s are great planes both to build and fly. Now, here's the question - I have an OS 70 4 stroke. Would it be better to get the 40 or 60 size star? We're not looking for 3D type performance - just something he can do basic aerobatics with and fly around lazily when he wants to. I have a GP Ultimate to put together whe he gets ready for more advanced stuff.