I autocross and go to time trials with my '94 daily driver. Now has ~85,000 miles and one notable off road excursion. Driven enough to go through OEM, B3#, R4S, R4, EBC pads to see the difference. Same for MXX3, XGTZ, Kuhmo, and full race tires. My only limit to brake comments is two systems - OEM and 40mm rears.
The stock brake system is unbalanced. While safe because the fronts do most of the work anyway, it isn't very comfortable. Having a balanced system makes a huge difference. Properly sized calipers is one way to get there, and an ABS system is electronically giving you a balanced system.
Yes, I make and sell calipers, so install the bee ess filter, but I can relate the same stories as Chuck when people say "Holy ****, you don't have ABS?" I especially like the ones that follow me into turns but not out of them. Braking is 90% balance, 10% size.
Without ABS, the biggest adjustment will be learning that you achieve maximum braking in a straight line. Ignoring rain, dirty road, etc, non-ABS is slightly less effective in turns. Conversely, if you become skilled with the car, the rear braking can help rotate the car during corner entry.
If you keep the same master cylinder, more brake caliper piston volume will allow better modulation. Basically you have to move the foot pedal more to fill up the space behind more/larger pistons.
Finally, think this through - a BBK isn't really going to have substantially more clamping force applied, if any. Your deceleration rate is dependent on the tire friction against the road surface. If a brake system applies enough clamping force to lock up a wheel, more clamping power doesn't slow the car any better. The only way to slow down faster is to get all four wheels to reach imminent lock up simulataneously.
Another thought experiment about BBKs: you will gain a huge huge huge amount of clamping force with a 4 piston rear caliper - but then you will keep the rear caliper from applying 75% of that by dialing down the adjustable proportioning valve. If you didn't, you'd be locking the rears instantly.