When you are researching buying a mac there are a few things to consider, one of them is speed. There is a great site by primate labs which collates speed tests according to model and ranks them. This was useful for me when I was thinking of upgrading my Mac pro to a new Mac mini, only to find that my four-year-old Mac pro was faster! Check out how fast the new mac-pro’s are - insane – I wish I could justify buying one!
Another very valuable site is everymac.com which compares each Macintosh model with the models that came before and after. It helps you see any subtle differences between models. The ‘what are the differences’ section at the bottom of each model is particularly informative.
Finally, there’s the official Apple specifications page which can also come in useful, although I prefer everymac.com.
If you want to see how long a particular model has been in circulation check out the mac buyer’s guide run by MacRumors. This gives you an indication of whether there might be an upgrade soon.
Once you have decided which mac to buy, don’t’ forget that you can get refurbished macintosh computers from Apple.