The way I see it is not the carb size, it's the needle size required to work with it, get the right needle and you could effectivly run any size carb on any size donk.

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If in doubt ask

The theory with a SU is that the piston is supposed to open as far as it is needed. So you should have full opening at full revs (under full load) If you carby is too small it will be fully open before you hit the redline and you run out of puff (as well as running out of needle)
If the carby is too big it will not open fully at full power and this means that you are only using part of the needle.
So you have to work out what needle you need based on only using part of the needle!

But.... If you are using the car for something other than circuit racing (say in motokhanas) the wrong carby may work out to be the right carby. When you need big torque and not not high revs the big carby may work. (but it also may not!)

I have about 100 different carbys here and I am running a single 1? su on my 1100 by choice! It all depends on what you are trying to achieve. I am trying to achieve fuel economy in a daily driver that rarely goes over 50kph.

That is an excellant summation of what was already said.
Not having a shot - just saying the above