To be honest, I'd be surprised if the Enterprise could withstand a series of MACs even with their shielding, though, a photon torpedo would likely vaporize the Infinity before it had a chance to fire, assuming Kirk would do that rather than jumping to warp. Curiously, I think the UNSC would be able to track the Enterprise and pursue. I'd have to give it to whomever decided to go all-out first, but the Enterprise could definitely be quicker to the draw.