I own an EX1, when it first came out, I would use clip browser to convert to .mxf.
Since V9 is out, I use the EX1 .mp4 file.
At first, I would grab the .mp4 with "device explorer" but after a while , I would just search all .mp4 file on the card and copy them, which is faster for me.
I have noticed that projects involving .mp4 files with some 18 hours of footage on the timeline worked very well from Vegas. Occasionally, I would have a few .mxf files, 10 or so and at times these would have the red frames but would still play ok.
Recently, I just loaded a session with about 6 hours of .mxf footage on the timeline and then after 10 or 15 minutes, Vegas would suddently be slow and non responsive for about 30 seconds and I did get several more occasions where handling .mxf footage was memory intensive.
I have a Q6700, 6gb ram with Windows 7 64bit and V9 32bit.
Use to be Vista 64bit with V8, then V9.
Handling .mp4 in Vegas works like a charm!
But mxf seems to be handled differently and more memory intensive?
I've only experienced issues like this when Vegas is a) reading from a slow device (IE my USB2 drive), b) streaming lots of data from a device (a single DV AVI loads up pretty fast, but when I had ~30 of them in a project it takes a few seconds for Vegas to get focus again) or c) something is encoded heavily.
Pretty much anything besides DV AVI counts under these three conditions.
Did you try unchecking the "close media files when not the active app" in the preferences/general?
Don't know if this is relevant, but I have noticed the same thing--long pauses--not only in Vegas but other apps as well. I am running Win7 Pro-64bit. My system usually has 4 to 6 hard drives attached at any time and I have noticed that if you access info on a drive that has not been "active" for some time, there occurs this pause. I suspect that it has to do with some power-saving scheme. Hope this helps.