...I guess I'll start off with my thinking...
My 73 started with a 17mm MC with stock brake lines. I was experiencing spongy
brakes. After replacing all the lines and rebuilding the stock calipers and replacing
all of the fluid and a proper bleeding. They felt inadequate during a spirited ride
through the Cascades, when I lived there.
I replaced the stock lines with steel braided teflon and changed the 17mm MC
with a 19mm MC. The brakes improved, but the feel at the pedal was more
compression was required (travel).
I have read, more times than not, that the steel braided lines are breaking at the
crimps and leaking causing brake failure. I ran them on my 73 with no problems
from 1990 to 1997 until I scrapped it. I have been thinking of running stock lines.
Have never heard nor read a problem with them...

I am considering a 23mm MC, but I have two questions.
Is there a length difference in the housing (mounting flange to body fwd end)?
With the increase in volume, will the pedal travel increase over the 19mm MC?

With the 19mm MC, when I entered a fast corner, I was able to simply roll my
ankle over and blip the throttle as I down shifted while under breaking.
The pedal travel would allow the brake pedal to be parallel (coplanar) with
the throttle, at that position.
When driving the 72 911, (with a 19mm MC), the brake travel under braking was
less and the brake pedal position was above the throttle, forcing me to
heel-toe, rather than the opposite as in the 73 914. Granted the 911 had M
calipers, while the 73 914 had stock calipers.
Now my 74 914 has Brembo AMs on the front and stock rears.
I was thinking that the 23mm would be better suited to the Brembo AMs, or am
I incorrect in my thinking....
...all inputs are appreciated,
Dave

The 23mm master cylinder does fit, but I understand you may have to play with the length of the piston rod. Are you going to use larger brake calipers?

As it will displace more fluid for the same travel, and you are not increasing the total volume of fluid in the brake system by adding larger diameter brake cylinders, etc., you will have less pedal travel to displace the same amont of fluid.

Unfortunately, you will have a pedal that is harder to push. You lose the mechanical advantage as you're trying to push the same amount of fluid (I don't recall the formula for volume of a cylinder, but you should get the idea).

...I purchased PMB performances Brembo AMs...they're beautiful, by the way.
I remember reading a chart of the clampping pressures and the 17mm created
more pressure than the 19mm. I don't recall what the 23mm measured.