I'm not sure what T.R. is, but we ran a tandem SAW rig back in the shipyard. Lincoln LT-56. Quite a large machine as compared to the LT-7 tractor, but wouldn't it put down some wire. We averaged about 65 in/min. travel. The machine rooted with 3/16" and filled with 5/32" wire. Always seemed kind of backwards to me, but I worked quite well. It would fill and cap a 3/4" plate in 1 pass. Joint design as I remember was a 3/8" land, 30 degree bevel. I can't remember the amperage or voltage parameters. I do remember it was very picky as far as any type of gap in the root. No more than a 32nd? maybe. It's been so long since I've run one of them.
I think we also had an LT-7 tractor set up with 2 electrodes side by side, running 1/8" wire. But as I said, it's been more than 12 years since I've run one.
I'm sure Lincoln could steer you in the right direction.
I wish I could be of more help with the GMAW, but I never did anything concerning GMAW running in tandem.
I can't imagine a GMAW unit outperforming SAW.
Hope this helps.
Dale Simonds