As per Neals info - my understanding is 10inch props on 3s and 8 or 9's on 4s.
Rc timer props fly bloody lovely. They needed a bit of sanding - but my 450 is super stable with them. Also price is good as is free shipping
On my 450 - with 2216 motors its a rocket - I've never tried it on 4s - I suspect it would be far too quick for me. I'm sticking to 3s.