There's stretching for the look and then there's stretching for clearance. I'd only do a mild stretch unless you have very low offsets or very wide wheels. If you want that "cool" look that a lot of the hella flush people are going for then a 195/35/18 on 9 and a 225/35/18 on 10.5 will give you a big stretch. It looks cool but its not my style and I think it looks a little ghetto. I only like a little stretch. Plus on more extreme stretches and depending on where you live, in the winter you may have to worry about the bead coming undone.
http://tyrestretch.com/
Heres 9 on 195 but on a 17.
And 225 on 10.5 on
I plan on running 235 on 10.5 if I ever get new wheels which is in between extreme and mild.