I went for the CA because it fits in the 1200 engine bay a whole lot nicer (from what i've seen) without the need to recess the firewall or have the intercooler sticking through the grill.
CA's are a whole lot cheaper than SR's, and while there may not be as many of them, every man and his dog that owns a CA powered 180sx or silvia is upgrading to an SR these days which means that there are heaps of unwanted CA's laying around.
Its possible to get 300rwkw out of a CA, (fairly comfortably) which is waaaaay more than neccesary for a street car, so why go through putting a SR in when a CA will do?
The only thing i haven't really looked at is what it will cost to build a 200rwkw SR compared to a 200rwkw CA.
Please pick this comment to bits if I said anything wrong.