with 2009 macs you should be able to get 6-8 layers of 1080p with AIC codec
i get 6-8 layers on my 2009 8 core 2.26Ghz mac with AIC 1080p 25fps
2009 macs with 10.6.x are significantly faster than 2008 with 10.5.x
around 20-40% faster
with 10.6.x more cores have improved performance - more cores are better.