To preface, here are my system specs:
16gb Installed RAM
Win 7 64bit
Nvidia 560m 3gb
OCZ Vertex 3 SATAIII SSD 120gb
WD Scorpio SATAIII 7200rpm 750gb
The project: Music video with 1080p footage scaled down to 720. All non-used footage has been deleted, and the project has been completley purged prior to rendering.
The problem: Every time I render (h.264 CBR 120 w/ audio), it gets about 1/4th way through very quickly and then slows to a painstakingly slow chug. In 15 minutes, it gets through a quarter of the project with an estimated 50"ish" minutes to complete, but the render time quickly doubles...and now I'm at 5 an estimated 5 hours to complete.
What gives? I have, from what every guide on the internet has said, optimized AE for my machine....
You're rendering to the wrong codec from AE. Render to a production codec and then use Adobe Media Encoder to compress the file. You could also just open your AE project directly in AME and render your compressed footage there. You'll get a much better result, be able to do multi pass encoding, and save a bunch of time.