I just did my first ever 4 challenge modes last night and got gold in all of them with relative ease with an avoidance build. Our dps warrior was even using an int flask and we still had plenty of time left. :-)
Had no trouble getting golds in avoidance build (using my normal raiding gear - so no working meta, etc). With the pre-nerf vengeance levels still active in C-modes my damage was pretty ridiculous considering the gear scaling.