(Thank God it's only the 3rd Key for Guts, cuz 4th key basically near-stomps)
Guys, i need clarification because I looked at the calc Guts scales to for Durability, and it's either base-line 8-B or 20 tons. Confused. I'm going to assume Baseline for now--cuz if it IS 20 tons, it might not exactly be a fair fight for Buggy.
Okay, it appears to be that he took a 9.66 Ton of tnt attack (and wasn't all that hurt by it. Should be High 8-C, but considering a small bit of the feat was not seen, base-line 8-B is understandable--so technically 11 Tons). Buggy is scaled from tanking his own Buggy Ball (the value halved) so he has 6.777 in comparison to Guts' 11... Nearly double.
I suspect that Guts will cut down Buggy, but Buggy will pull the trick he used on Zoro to back-stab Guts, injuring him. However, Guts is a beast in endurance, and after realizing that his blade is no good, he will use his cannon, his sword as a blunt tool, and his multitude of weapons (explosives, arrows, etc) until he finds the most useful tool.
Buggy however will not be helpless, he will respond in kind with his DF and multiple hidden weapons. Even if he managed to use the Buggy Ball, it would only serve to hurt Guts a bit, and not take him out of the fight.
I feel like the battle will not be a short one, but over some time, Guts will prevail and slam Buggy to the ground after sustaining some injury due to Buggy's ingenuity.