I kid you not: This sucker weighs about the same as a Speed Graphic! (Shipping weight on the box was 6.0 lbs, of which I figure no more than half a pound was packing materials.) And I only get 1/4 of the image area.
I know it weighs more than my 35mm SLR however, cannot comment on the Speed Graphic (also own) unless I get them out and weigh them both. I have used the 645 w 1.9 and finder w built in meter doing aerial photo graphs from small plane. Of course sitting in a plane and holding the camera is not the same as walking around, although I never gave the weight a thought so it did not bother me. YMMV