I took my 4 Hunter/1 Priest team (lvl 70) to UK last night and did...ok. I took out the first boss after a couple of wipes, mainly due to poor pulling technique, but had no trouble clearing up to that point. I then cleared up to boss #2 (&3) but was trounced and decided to return at 71-72. I'm mainly wearing BC blues with the scourge event purples and get a tooltip dps of ~400 on each hunter. I'm also using cunning pets instead of tenacity, so I may try to get bona fide tanks next time. I also ducked into The Nexus and cleared out one wing (no deaths) but was thrashed by the caster lady when I failed to look up her specific strategy =)

I think a 5-person team with "average" BC gear could handle UK right out of the gate, but there's a much smaller margin of error for boxers, due to the increased mob dps (much like BC). I'm guessing I could clear the whole thing by 72, assuming I put some minimal effort in to getting some new enchants, etc.