I've done dozens of upgrades, just none quite like this one. Main ? was using 2nd lug to go DIRECTLY to other blg. On cable size; yeah I can reference the table same as anyone; thought someone would know off the top of their head. Existing service is 200a. H/O added attached garage, 24 x 24 addition, heated swimming pool, hot tub, and lots of landscape lighting. Pole blg is for auto repair and restoration shop w/ welders, compressor and of course lights and receptacles. Did I do a load calc, on NEC embossed paper, no. Who here thinks upgrade unnecessary ?