This afternoon I had some time so took the 5D with Tamron 28-75 (my alternative lens for this range--have 24-70L also, but often prefer this one which is very sharp) and the G1 and 14-45--plus the FD 35 f/2.8 and did some comparison shots on tripod.
I expected a difference in DR--and there is some, but shooting RAW I am able to compensate for that, at least in these shots. I shot at 14/28, 24/48, 35/70 at base ISO 100 and comparable f stops, center focus. I had tried a few briefly when I bought the G1 but nothing with foliage/finer detail (it was winter after all LOL) but I have to admit, I'm impressed.
I feel the G1/14-45 requires a bit more care in the processing--and def. capture sharpening. I haven't printed these, but plan to but expect for others not to be able to make much distinction. Actually, I liked how the G1 handled some colors better even though I use camera profiles for the 5D (strictly personal opinion).
I also shot with the 5D at 70mm and used the FD 35 f/2.8. The FD needs a bit of contrast boost, but otherwise is def. a good competitor. All in all, I feel very good about shooting with the G1 in good light. I need to do some interior shots, low available light. I know that the 5D will do very well, but I'd like to have some kind of baseline for myself to consider when/where to pull out the 5D and fast lens.