>I do greater than 50gig files in Premiere and Vegas Video all the time,
RAW format yes but not MPEG2
Here's what I said before and in short, there are several types of MPEG and they are all different, for video the most popular are MPEG1 and MPEG2 and MPEG4 and of course MPEG3 for audio.
There's a big difference between manipulating and editing MPEG video. There's also a big difference between MPEG1 and MPEG2.
MPEG2 was never intended to be edited, MPEG2 was intended to be rendered from RAW streams and that's it, it was never intended to be an open codec. MPEG4 for example can be a closed or an open codec but MPEG1 will always be an open codec. Divx 5.0 for example which is an open codec uses a different MPEG4 algorithm than Microsof's MPEG4 v7 or v8 which is a closed codec. Divx 3.11 for example was hacked into an open codec which is from Microsoft's MPEG4 v3 which is a closed codecs.
The MPEG2 codec is not free and contains proprietary codec algorithms, different MPEG2 codec algorithms can be made by several different companies, no matter what editor you have (well >$5000 anyway) even the worlds best MPEG2 editors may not properly work at editing certain MPEG2 algorithms or streams, they may work for some and not for others. For instance I use the main concept MPEG2 codec that's included with Vegas Video but my ATI-AIW capture card captures uses the Go Motion MPEG2 codec. All editors will 'do their best' at editing proprietary MPEG2 streams. The more complicated the algorithm of the MPEG2 codec stream is the more difficulties MPEG2 editors will have at decoding the proprietary algorithms because of this problems can vary from out of sync clips to program crashes, or whatever... The bigger the file the bigger the problem.
This is not a problem with MPEG2 editors, it's the nature of the proprietary MPEG2 codecs. In the end, unless you put down $25,000 down on a professional system, there is no guarantee anything will work.