For those looking for a solid upgrade for the stock CTS-V2 look no further than the 9-309-1039 pump kit from DeatschWerks.
This kit not only provides a significant increase in flowrate (approx. 25%) vs. the stock pumps, it also allows the functionality of the GM fuel module to remain in place. No low-liquid level concerns with this arrangement.
This kit has shown to support 750RWHP on E85 when used in DeatschWerks CTS-V2 test car. That is a major upgrade vs. the stock pumps which have a hard time keeping up with a stock LSA engine on E85.
The swap is straightforward and takes 30-45 minutes once the fuel module is on the bench.