I've gone for the 4AGZE with a turbo. Its lighter than a CA or SR, small, there are heeps of parts, they're cheep and you can get a lot of power out of them. Oh yea and they piss off all the "keep it nissan" guys. If money was no object I would like to get two 1.3 Hayabusa motors and get the conversion that lets you make them into a V8. 2.6ltr V8 with huge hp and 10,000rmp, how could you go wrong?!! (check out this link
http://thekneeslider.com/archives/2005/02/09/hayabusa-v8-engine/ )Realisticly though the A15 is probably the best budget option and you don't need a huge amount of hp to make a 1200 go well.