as 3.06 ghz imac no problem, it will run well at home.
I use QL spaces for nearly a year but Altiverb and Sonnox reverb.
each is different, for my part I find that "spaces" reverbs offer very classy, much warmer qu'altiverb and they make a good impression "3D" with mixes. The reverbs like "hall" are particularly successful, and the "rooms" for drums (which I use in many cases other than batteries), the big reverbs "churches" also work well (but that was with both Altiverb).
The nice this plugin is that you can quickly know the different presets and color they bring, the utilisaion is very simple., Forcing the disadvantage is that you can not set the reverb wish (dry / wet control, pre-delay and off you go ..). It gets annoying on presets like "flat" etc. .. to work and very limited vote.
In the end the reverb is really worth because it brings life into the mix and a certain class (right now I recognize it as a very subjective comment ..), I find it a color all its own.
If I am not 10 is that we recognize we may be limited by the lack of adjustable parameters .. on that side of the Sonnox reverb has everything you need and no shortage of heat.