you are correct in your assumption that you need to specify what turbo...for instance..
I'm running a TD05-14g...now at 15psi this turbo will almost flow 500cfm's, then I ported it..now it will flow 500cfm's...well if I try to put that 500cfm's into my D-series...BANG!, no more D-series, now if I take say a TD05-12a,which flows 320cfm's@15psi...I can brag about running 15psi...but I'm making the turbo work outside its optimum efficiency. So find a turbo that will match what you want your car to do...if you need help,ask...I have almost every turbo compressor map known to be...I can match a turbo to what you need...mathmatically....oh btw...I'm running a 14g@7psi intercooled...about 300cfm's...but the turbo is working at 77% efficiency. B)