I am upgrading my Avid 4896 Pro for two main reasons - Rigidity and ATC (out of the box).
A 5x10 unit from either Camaster or ShobSabre is only a couple of grand difference from the 4x8 models. However, the extra footprint will make it a VERY tight fit. I am trying to gauge how many people wished they had a 5x10 after getting a 4x8. For me, I have had to pass on a couple of larger slab flattening requests, but that has been it so far. Mostly, I carve and do sheet goods. I would be nice to be able to put a 2 x 4 jig fixture at then end since I use the vacuum for sheet goods.
I am still weighing the pros and cons of the two manufacturers, but that choice is coming down personal preferences as both are great from what I am hearing. The one caveat here is that the ShobSabre IS510 won't fit through the garage opening without disassembling the gantry, which they tell me they really wish I would not do.