During last season I upgraded from -08 to -10 it made a big difference in cooling. -10 is like 25% bigger diameter than -08, it also helps to make sure there aren't constrictions in the lines. Before going to -10 lines I took out the mocal thermostat hoping that would do it, but definitely the bigger lines helped. You might just go straight to the -12's recommended above.

I still have to also drill and tap my adapter plate to use 1/2" fittings - that's the last constriction in my system.

Jason.