I recently ordered the polar turbo kit as well. I was planning on running the Pulsar 4849G (G25-550 equivalent) and after chatting with Polar he suggested the 5449 (660) setup due to the smaller turbos being almost to efficient creating large torque peaks rather low in the RPM range, which is not very friendly to rods. My goals are just around the 500ish mark and he said either turbo should hit that on pump gas and surpass it.