I agree on the weight issue, but think the bulk one is more of a problem. I use a Bender 4x5 when hiking, and have found that if I leave it on the rail, then it requires a large bag and is too bulky, and if I take it off, the process of dealing with a floppy camera gets to be frustrating, since the field is full of (surprise) dirt. The issue for me has mainly been that I need a bigger bag, which gets ungainly on uneven terrain. I find that dealing with the bulk and setup time once there (reassemble, and reorganize the bag so that what I need it near the surface, rather than compactly packed) gets to be a bit daunting when deciding whether it goes out.
This being said, I've packed that camera from the NJ coast through Canyonlands in UT, and continue to do so. One of the best decisions I made about it was to get small lenses; a 203 Ektar and a 135 symmar weigh less than the camera bag, were relatively inexpensive (less than $400 for the pair), and are very sharp.
What about a quasi-modern, flat-bed, Burke and James, if the Tachihari or Calumet doesn't fit your budget?