Got to be honest, it's not close at all here. My money's clearly on Gadget and Iron Man, and it seems that everyone is in agreement. Though I wouldn't be surprised that it's because no-one really knows who Kamen and Gat are. I didn't know who Kamen was before I read up on him to be perfectly honest.
Kamen's got wind, which will be extremely counter-productive to Gat's accuracy with his weaponry, especially his guns. It might blow Iron Man off course a bit, but Iron Man's thrusters can easily adjust to extreme conditions. The only way I can see wind having an effect is blowing Gadget over, and even then, Gadget has gadgets to protect himself, and Iron Man to help him out. Kamen does have A LOT of speed though thanks to his vehicle, so that may pre-occupy his opponents.
Gat's basically a guy a human who's got super strength, pretty good with explosives and guns, but he's hot-headed and I generally can see him getting pissed off at Kamen due to his use of wind. Really a guy that would work better alone and not in a team.
I'm not going to go in-depth on Iron Man so I'll say this: He's a past Battlezone winner. Let that sink in for a minute.
Inspector Gadget may be incompetent. But I see Iron Man as a Penny here. Inspector Gadget compliments Iron Man's need for upgrades should the need arise, and Iron Man is the guy to carry Gadget and carry out the majority of the offence. Even if Iron Man is knocked down, Gadget can still hold his own somewhat, and Iron Man can still fight strongly without Gadget.
Iron Man could beat Johnny and Kamen alone probably. But with the assistance of Gadget, and keeping him in line, this'll be a walk in the park. Inaccurate C4 and wind simply won't be enough to stop Iron Man, let alone both him and Gadget.