Ok, based on the info you've given, I'd say you have a 64.385% chance of victory. Plus or minus 40% due to unknown factors.
64.385+40=104.385% chance of victory?
Seriously though, DF has way to many random rolls to even hope to try to give you a percentage chance. I mean even when people were doing controlled tests in the arena (same exact starting positions with the same units, same skills, same equipment, same everything) there was often still a wild variance in their results. After all you could always end up with a scenario where a thrown fluffy wambler kills a Bronze Colossus or you could end up where the FB kills everything and comes out unharmed.
To get a view of exactly how much randomness is here you could visualize a dice roll. If I want to know my chance of rolling a 1 on a 6d, it's simple (16.6%). Now I'm going to roll 10 dice and I want to know that chance of me rolling three 1's, two 3's, one four, and four 5's. Still possible, but it would take a lot more work to figure out. Now imagine two players facing each other trying to roll higher. If every time player 1 rolls a 5 or a 6 they get to roll another die and every time player 2 rolls a 4 they get to roll another die. What is the percentage chance that player 1 beats player 2? Even more complicated. Now imagine the same scenario again but this time you don't know what numbers player 2 gets to roll again on, or even how
many numbers player 2 gets to roll again on. That is combat in DF. Unless your name is Tarn Adams, or maybe a few others who have used hex editors to puzzle out the equations, it isn't even
possible to figure out the equation, and even if you do you are talking something with trillions of possible combinations that would take forever to figure out. To put it simply, giving a percentage chance of anything in DF is simply
not possible