At this stage it's not really a question of quality, more of efficiency. You can basically get 720p video with no noticeable artifacts on the old Apple TV, but the file sizes are bigger than they would be if you tailored the encode for a full-fledged computer because the old Apple TV can't keep up with the more processor-intensive decoding operations available. I would assume that yes, the new Apple TV will be better at things like CABAC entropy encoding which would often trip up the old Apple TV at 720p but plays smoothly through the iPhone 3GS/4. But I would definitely wait until it comes out before doing too many encodes. Then you can either experiment for yourself or see what happens with the Handbrake profiles (noting that there is some disagreement among the Handbrake devs about whether certain of the profiles represent the best settings for certain types of encode).