Ahaa I think I am beginning to understand, thanks to everyone for your input. So K16/24s & upgraded wastegates it is then.

 

Just to add a little more info, in 3 different cars I checked the stock spring in a K24 was set at between 6.9 and 7.1 psi opening pressure. The evo springs need to be set from 11.5-12.5 psi to produce 1.2 or so bar at wot