Well I think another problem is going to occur from this rather than xp/hr rates from bgs. If you have 10 toons in WSG, ALL your the toons on your team is in one location. You'd never be able to cap the flag as they could just have someone standing right next to your flag and continuely run it away from you.

In AB having 10 toons in one spot will be great for pushing but that doesn't leave much left to defend the other nodes. You'll probably never really actually cap anything but rather just go from node to node retaking it from the enemy.

In AV it might be okay since with 10 toons you can provide all the dps/healing and if you specced for it, tanking that you need. Although that's not till level 51.

EotS will be about the same as AB, but perhaps a little bit better. Again not till lvl 70.

SotA uses siege vehicles quite a bit, but might not be too bad if the other players get the idea to use the vehicles. Not till lvl 80 though.

Not even sure about the other BGs since I haven't played them.