Ronniemac,
It doesn't quite work that way, in fact the reverse applies.
Yes you would reduce pedal travel, but...
If you use a 0.75" MC, the piston area is 0.4417 sq in.
Piston area of a 0.70" cylinder is 0.3848 sq in.
So, you have applied the same `pedal force' ( a constant) to a 14.7% bigger piston area, which reduces the fluid pressure, (psi) and hence the braking force.
850s had a 0.750" master cylinder back in the early 60s, BMC changed to a 0.70" to improve braking and have used it ever since (except on Cooper 998 which had a 0.625" MC for even higher brake pressure).
It is the fluid pressure which determines the braking force, not the flow.
<edit> re the little valve in the brake MC, it serves 2 purposes-
1. Supposedly keeps a little pressure in the brake lines (I doubt this happens after a bit of use)
2. Makes it a little easier to bleed the system, by acting as a slight restriction as the pedal is let up.
I've run brakes without this valve fitted, but NEVER put one in the clutch MC..
