Not a question with a simple answer, unfortunately :-)

Yes, size does affect hardiness but only tangentially - it is the degree of establishment in the landscape that plays the biggest factor - smaller, newly planted specimens are unlikely to be as cold hardy as larger, well-established plants. Siting will also factor into the equation.

Since virtually all Japanese maples in commercial production are grafted and to relatively uniform rootstock, one could argue that any cultivar should be equally root hardy. When they leaf out is more of a concern - early to leaf varieties are more prone to late spring cold damage than those that leaf out later, variegated/fancy leaf or not.

If you read through the literature, there are several types that seem to be repeatedly recommended for colder location - 'Bloodgood', 'Emperor I', 'Fire Glow', the straight species (either red or green leaved) and most of the low, mounding dissectums. I'd assume the last seem to be tougher because of their low, groundhugging growth habit and the fact that they are usually planted close to structures.

If you have a good location in mind - one that provides the correct soil conditions and the proper lighting, is out of prevailing winds and has some shelter provided by surrounding vegetation or structures - I'd give it a try.