angular contact bearings - back to back, further apart

[johnsattuk]

I'd like for this design to offer as much stiffness as possible, will it work, or is there something I'm missing?

Some car differentials and wheel bearing designs have a single use deformable spacer tube between the bearings. It has the advantages of gripping both sides of the bearings, the compressed tube and the tensioned shaft add to the stiffness of the assembly, and the high bolt up torque required to deform the spacer, make the nut more secure. Usually adjusted by measuring the increase in torque required to turn the spindle whilst tightening the nut.