Rear brake upgrade / brake bias

[mikehhhhhhh]

I just want to sanity check my plans before I spend my day tomorrow removing my old four pots and more importantly, getting rid of them. 

Right now I have Lotus spec AP 4 pot on 308mm fronts and standard Brembo rear on 295mm rotors. It's clear to me that the braking is not right - I guess too front biased, which means they lock fairly easily and the car dives a lot under braking. 

I far prefer the braking of a friends car with standard brakes and upgraded discs, although that's still not perfect, especially in the wet. 

I found the BOE article suggesting the Elise works well with a ~55% static front bias, so I've picked up some lotus motorsport rear callipers with 38mm pistons. (Standard rears are 36, standard 2 pots are 44)

I plan to remove my 4 pots, and put the original 2 pots on the front.

According to a basic static bias calculator, this would give me 59% front bias. 57.5% if I stick 308mm rotors on the rear as well.

4 pots front and the old 2 pots rear would give 56% front with the same size rotor, but would that require a master cylinder upgrade? Has anyone tried it?

Am I missing anything else that the four pots are offering me, though? Does anyone else run with 2 pot front and rear? 

Obviously, ideally, I want to be running a balance bar pedal box, but I've yet to settle on anything to do that yet, so I'm just looking for a short term win initially.