Noel Borthwick [Cakewalk]
The default time stretching at playback is preview quality. However when you bounce it will use higher quality stretching. The settings for stretching are in the clip inspector.
You can get even better quality stretching by first converting your clip to an ARA clip and then slip stretch it. It will then use the melodyne stretching algorithm which sounds really good even at playback time.

Thanks Noel. This is exactly what I was hoping for.

>>No wonder offline is the only way to get a decent rendering.
Check out slip stretching with melodyne region FX clips. You may be surprised how clean it sounds. I've even done pretty drastic stretches and it sounds usable during playback.
 
>>Or is there some other way to create an ARA clip?
I meant creating a Melodyne region fx clip. Same thing - just time select a region on a clip and press CTRL-M