Single Piston vs 4 Pot Calipers

Difference between the 57 and the 40/44 combination piston areas is 9% the major difference will be the dics and pad area - however if you have increased the m/c diameter then the line pressure will be lower so the braking for a given push on the pedal may not be as effective.

With such a low increase in piston area I would have left the M/C alone.

I asked a thread about this regarding a different, yet strangely similar question.

forum.retro-rides.org/thread/179517/exactly-influences-braking-power

As said, the total piston area accounts for the stopping power. In a sliding single piston caliper the piston will account for two pistons; 2 of the pistons in a 4 pot system opposed their relative pistons.

That formula that mk2cossie alludes to is:

Applying that to your scenario

Mercedes Brembos

Average Piston Diameter = 42
Average Piston Radius (r) = 21

TPA = 3.142 x 21 x 21 x 4
TPA= 5541.77mm squared

For what's on the car now:

Piston Radius = 28.5

TPA= 3.142 x 28.5 x 28.5 x 2
TPA= 5103.52mm squared

However, I've had better pedal feel myself with single piston calipers strangely, and on one car a specialist was dead right about it, even with the new owner changing everything only to have the same result. That was for my 944 S2 with braided brake lines on stock Brembos and 944 Turbo on refurbished Brembo Big Blacks from a 928 GTS. A friend with a Nissan S14a noticed a similar thing.

BUT, in your case, your TPA means you should be fine with your existing master cylinder, and with the bigger pad and disc should yield better brakes with a similar/improved pedal feel.