I would actually stay away from Guarder springs for the Hi-Capa. The hammer spring at least. I've seen two separate cases where a Guarder Hi-Capa hammer spring weakened significantly to the point where hammer strikes were irregular. I haven't heard any complaints about the recoil spring though. If you're looking for both springs in a set there's always the King Arms 150% set to consider.

The loading nozzle is prone to breakage in Hi-Capas that have metal slides, enhanced recoil springs and shooting propane. The added pressure tends to be more than it was designed to handle - upgrading to a stronger one is recommended.

I personally like using the Shooters Design POM cylinder unit.