Originally Posted by Kontact

To be clear, I put an 8/9/10 hub in the space of a 7 by copying the dish from an 11 speed up.

When Shimano introduced 8, the went to 130 and moved the inner cog closer to the right flange. This resulted in the dish of the wheel being identical to 126mm 7speed wheels. (The hub bodies usually were identical, just the freehub and axle/spacers having changed.) When they came out with 11, Shimano gave up on their previous dish standard and made room for a wider freehub by moving the hub body to the left, eliminating one left axle spacer and losing some bracing angle in the process.

What I did was shorten the axle on the left and re-dishing to the 11 speed standard. That made just enough room for the 8/9/10 freehub while staying at 126mm. Shimano was too conservative about dish to do that in 1989, but apparently not so concerned about it in 2012.

To go to 123mm you might be able to shave 1mm on the driveside, depending on your lockring and dropout, but you'll definitely need to take 2-3mm off the left side - which means further dish is required. I'm not saying 123mm is going to be perfectly fine, but it will be much better than trying it with an 8/9/10 freehub. It won't be as solid as even an 11 speed hub.