Don't wanna hijack, but have any of you who've done this measured speed gains in real-world tasks?
Although the 2008's are behind on processor speed, I'd think that using an SSD might make the 2008 seem speedier than a 2011 for some tasks that aren't processor intensive, like PS filters or video conversion.
And the irony is that it's progressively more difficult to replace stuff in iMacs as they get newer. Bottom line being whether a used 2008 with an SSD is better than a newish 2011 without?