Good question, I wondering myself about Bishop's limit. Could he drain Superman of his solar reserves by sucking up radiation directed at him by Supes? Can he abosrb and re-channel the radiation from Green Lantern's ring?
On the other hand, I seem to remember Bishop reaching a point where he was overflowing with energy after Magneto froze the X-men with his magnetic powers. As a result, Bishop began re-channeling this energy back on Magneto but was interrupted by Colossus right at the moment when Colossus abandoned Xavier's dream.
i don't think Bish. could handle the Power Cosmic. Surfer could warp space and attack him with hyper speed cosmic power if he wanted to. Bishops cells wouldn't be able to process the transfer fast enough.
However if the shoe were on the other foot and Surfer used Bishop as an amp. I think Surfer could control the exchange causing no damage and Bishop would become a universal mirror that could be strong enough to expand the universe. Much like surfer teamed up with the molecual man to stop the beyonder in seceret wars 2, surfer may be in league with The big Ones, like eternity, death, tribunal, beyonder...