Compilation time for Quartus II 9.0

To be honest, it's worth installing and trying for yourself. (Luckily, Quartus II plays quite nicely when having multiple versions installed, although I've heard complaints about SOPC builder, but I don't use it.)

The reason I say that is it's very design dependent. About the timeframe you're talking(7.2 to 8.1, I don't think there was a 7.3), the physical synthesis algorithms were improved a lot, so that easily could be the gains you see.

Linux versions were also greatly improved(they were actually far behind windows for a technical reason, and were moved to being close to par).

It also depends on what family you're targeting, as older families generally won't see specific algorithmic impromvenets, just generalized improvements(like the Linux improvement). I don't think 9.0 is going to improve as much, but it's worth trying to find out.