I just thought I'd do a quick 'show and tell' on the RCT800 Hexacopter frame which is available from RCTimer for a very good price at $59.99. At this price and from what I've seen so far, I may just have to add one to my collection.
It's a surprisingly large copter at 80cm motor to motor distance which allows the use of some 14" props for serious amounts of power. The good thing with the arms is that they are also compatible with the 450 frames, which would allow you to fit upto 16" props on a 450 style quad put together with these arms. The extra length does of course make them more prone to flex and wobble, but nothing too bad.
My friend Guillaume has put his together incredibly using 6 2830-14 750KV motors spinning 14" props on 4S!!!! This just shouldn't work, but somehow it does and it flies remarkably well, with no noticeable heating of the motors (this might change in summer, but it's currently winter here in the Alps and the outside air temp is quite low) and it comes in at ~2kg complete with a 5000mAh 4s lipo. With this setup he is getting about 10 minutes of flying time, with quite a bit of aggressive flying thrown in.
Here's a couple of photos and a video of the RCT800 in action.