It's not necessarily about "what speaker size" to get, as it is more about the speaker and cabinet design/construction.....
If you are looking for a 210, absolutely get the Eden 210XST. Why? Because the frequency response of this little Cab is broader with accentuated low-end response and it kicks!!!
With the 800B, you will get 880W+ in bridged mono. I would suggest you stick with the 8-Ohm Cabs for this reason. With 8-Ohm Cabs you have the flexibility to add more 8-Ohm Cabs without running the amp into it's minimum load rating quicker with fewer 4-Ohm Cabs. When you have the flexibility to run more Cabs, you can push way more air and get way more coverage if and when you need it. I personally wouldn't settle for anything less than having that flexibility.
Remember, it's not the Watts that give you the coverage, it is the right set-up of Cabs. You put a 210XST(8) and a 410XLT(8) bridged out of that 800B and you will be way more than impressed with what you hear, I gaaroantee!
