I think you're really going to need to find something to fix that Vdroop if you're going to get any further. 1.47V for 3.4 is asking a lot.
I don't expect any other component is holding you back, although you could check your 12V line (use HWmonitor).
You can also use VRAM sinks for the MOSFETs, they can take A LOT of heat through, I doubt that's what's holding you back.