that's funny, cause I've had the completely opposite experience.
I had the i760 for a lil over 3 months, and while it was a decent machine, I'd always had an inkling that the mogul/6800 was better. Once Sprint's prices dropped thru the floor, I decided to give it a shot -- and I have not been disappointed. The Mogul in most ways is simply -- better.
Keyboard:
I was developing some form of carpal tunnel on the 760 keyboard -- the keys are way too stiff. I text msg a lot and my fingertips were constantly raw. I used to keep my thumbnails long to reduce the pain -- yes, pain. Also, the phone-on button's placement over the 'y' key was beyond annoying. I would hit that thing at least once a day. Plus, if I tried typing fast, the keyboard couldn't keep up. This happened frequently; it would simply miss keypresses b/c the processor couldn't keep up with me.
All those problems went away with the Mogul. The keys are soft, there's nothing in the layout to interfere with my fingers, and the processor catches every stroke as I fly along tapping keys in a rush. Advantage: Mogul.
Performance:
First, who can not be pleased with 2x the amount of flash memory? (I know that's just with Sprint). But I know a few 3rd-party apps that have performed better on the Mogul (S2U2, WinVibe, PocketCM come to mind). Indicates a better processor. Advantage: Mogul.
Speakerphone: Loud (tho slightly blaring) on the i760. Simply too soft on the Mogul; tho I hear there are hacks to increase volume? Advantage: i760.
Misc:
Camera: marginally better (2mp vs 1.3mp) Slight Advantage: Mogul
GPS: (now) Advantage: Mogul
Buttons: 13 external buttons vs. 7; Advantage: Mogul
Keypad: It's nice having it, but why the hell doesn't it have T9 input? Dialing #s is easier, but quick txting would be great if it had T9. Slight advantage: i760.
Overall, my experience on the Mogul has just been better (it's been 1.5 months now). When I had both devices (during 30-day trial), I eventually didn't even want to use the Samsung at all; especially for texting. Quite prefer the Mogul now; and my thumbs have never been happier.