thanks for that - and I apologise for the hi-jack
I'm not considering changing my brakes at the moment but am considering an adjustable proportioning valve.
I too have those archaic 4 pot jag brakes at the front.
During the build we rebuilt them and they're the most powerful things I've ever had on any of my (admitted, limited selection of) cars. When testing them (the archaic brakes) out my brother actually gave me a head-rush by slamming on the brakes and stopping suddenly - even though this might be a reflection of the poor state of my circulatroy system rather than an endorsement of the brakes - they're currently good enough for me.
However, at the track I feel that the front is doing all the work, making the car squirm (?) under heavy braking, so am considering a proportioning valve to try to dial the brakes in a bit better.
So from my perspective the proportioning valve will save me having to muck around with the rest of the system.
LoBelly