I'm currently riding one of each. I rode the CB750 yesterday and I'm riding the CB1100 today. Not sure which one I'll ride tomorrow.
With regard to the ergos, they are very similar. The CB1100's footpegs are just a bit farther back than the CB750. Maybe an inch. As far as I can tell, peg height on both is about the same. I really don't see a great deal of difference in the ergos between the two. I owned quite a number of UJMs in the past and as far as riding position goes, both the CB750 and CB11 are pretty similar. YMMV, but I've never heard anyone else compare the Nighthawks riding position to that of a sportbike. I bought mine specifically because of the upright, standard riding position I was used to from my UJM days.
I consider the CB1100 to be sort of a Super Nighthawk. It's got all the things I love about the Nighthawk, with more power, greatly improved brakes and better suspension (and, of course, a much higher price tag).
I've only had the CB11 for 5 months, so I can't say much about the reliability, other than I've had zero issues with it. On the other hand, I bought the Nighthawk brand new 17 yrs. ago and it has been bulletproof. Other than replacing consumables (oil, tires, chains, etc...) it hasn't required any other maintenance,,,except for a stripped spark plug hole that I caused
Overall, I think both bikes are pretty similar when compared with everything else on the market. If you're looking for cheap and reliable, the Nighthawk may be your best bet. If you want upgraded performance, modern engine controls (EFI/ECU) and nearly flawless fit/finish (and you're willing to part with $$$s), the CB1100 may do the trick.
If the ergos are an issue, consider a higher seat, lower pegs, different bars. You can tailor either one of these to fit your needs.