So what size are people using for road or track and what type of feel do you get through the pedal

It also depends on your pedal ratio

I am using a landrover 90 master cylinder as they are cheap new with a 4;1 ratio on the pedal

Pedal feels like a block of wood as in very little movement between light touch and stamp on the brakes, able to lock all wheels with a good hard shove.

HTH

I've got 4.75~1 on my brake pedal

I am using the popular obp twin cylinder setup,5/1 ratio,pedal its very hard and lacks feel.i have tried variations on cylinders and different balance,if I was building again I would try something else.can lock wheels but too much effort and need my boots on,,,,

Tandem or balance bar ?

If tandem Rimmer Brothers are selling Girling Triumph dual circuit master cylinders on special offer or you could fit the popular Fiat cylinder.

If you have a balance bar set 0.625" & 0.7" are the usual choice