Byakuya was overpowered by Bankai Ichigo.
Grimjaw beat the crap out of Bankai Ichigo and put a beating on Hollow Ichigo.
I think Grimjaw will take it unless Byakuya got some sort of power increase we haven't seen. I really wouldn't doubt it seeing how bad the writing is in Bleach. I say it surpasses DBZ for ridiculous power ups for no reason. Oh.. wait. There is a reason. "Resolve." XD LOLOLOL