Well I was having problems getting the 480p video encoded with x264 and still be compliant. I eventually figured it out thanks to your helpful advice but then I was looking into it a bit more and it seems that with a bit-rate over 15mb the advantages of x264 drop off. Besides, 480p encoded to mpeg-2 just simply works when putting onto blu-ray format without having to jump through any hoops to make it compliant. Also, it only takes a little over an hour to do a 2 pass mpeg2 encode.

EDIT: It is also possible to encode in 4:2:2 colorspace.