First of all, play the rachmaninoff transcription version obviously.
Play with a metronome, and gradually increase the speed by increments of 5bpm. Within a couple of weeks, you'll be up by 20bpm from where you started and you won't even notice it

1) don't raise your fingers too high. Keep them low next to the keys.
2) Try not to press down on the keys ALL the way to the bottom. Press about 1/2 way. This one helped me ALOT.
3) make sure you're not stiff. Keep your hand very relaxed. If your hand is tired at the end, your technique is wrong. You should be able to play it back to back 20 times and not feel tired. I can't say the same of other pieces, but on this one, you should feel strain AT ALL EVER.
4) make sure your fingering is good. If it is not, then you will not have a chance.
As far as temp - I think this temp is ideal: