Here's what Todd Kopriva said in another thread: http://forums.adobe.com/message/3813422#3813422
"When the headless version of After Effects is called upon to render frames to serve Premiere Pro for a dynamically linked composition, it's just a single process---not the multiple processes that can run when when you're using After Effects as the primary application. Other resources (e.g.,CPU threads, RAM space, hard disk bandwidth, memory bandwidth) also must be shared with Premiere Pro in the Dynamic Link scenario."
So I guess that's the whole answer. In any AE composition that's resource-heavy in terms of CPU, rendering through Premiere is way slower - especially on an i7, which has 8 logical cores. That means you're using a computer that's 8 times slower and it makes a lot of sense to pre-render in AE before, as troublesome as that might be when you have 20 or 30 AE comps in your PPro project.
The "speed" glitch I had helped a lot, but didn't really solve it.
There's a way around that. Not sure it affects anything quality-wise. You just open AE and do a full RAM preview of the sequence. Then go to PPro and "render effects in work area" for that specific part of the project. If you go ahead and do alter the original composition you're gonna now it because the preview in PPro will be gone. A bit troublesome, but better than manually duplicating and pre-rendering 30 comps and having side comps with the actual effects as backup.
