Hmmm, weights, I know exactly what you mean there but that's something that should improve as more disc brake options come on the market. The Boardman Team Pro hybrid is billed at 20.5lbs with 700x28 tyres and disc brakes, that's pretty darn light:-
http://www.boardmanbikes.com/hybrid/hybrid_pro.html
if you want to get much under that, and have disc brakes and tyre clearances, then you'll be talking a lot of dosh.
IMO, if you already have a skinny tyre road bike for good weather, and you want flat bars and disc brakes, then you'd be limiting versatility if you aim for something that only has clearances up to 700x28...but that's me. If this is for year round commuting then I'd want to be able to put larger tyres, or studded tyres, on when need be in Winter.
I'm going to be guessing a little here but I wonder how much experience you have of a larger quality slick tyre. For example, I bought a Crosstrail Comp for my eldest and it was the wheelset from that I used to test out my 29er. First run was with the wheeslet as stock, so the 700x44 semi knobblies it came with. The rigid 29er felt much faster, nippier and lighter than the Crosstrail, I really noticed the difference on the front end. When I put the Halo Twinrail 2.2" tyres on I didn't notice much difference, they felt as fast and I preferred the feel, I really don't like those stock tyres though, horrible feel on corners. But then putting the 700x40 Marathon Supremes on was a huge difference, everything felt faster, and they're pretty light for a big tyre, about 500g each.
When I was commuting 40 miles a day my best average speeds were 18mph and 16.5mph on two different bikes:-
18mph - Giant CRS Alliance flat bar hybrid, carbon forks, half carbon half alu frame, 27 speed deraillers, using butterfly bars, and with 700x23 tyres, all in bike weight was 22lbs
16.5mph - Surly Crosscheck steel F&F, 9 speed hub gear, butterfly bars, 700x35 M+ tyres, rack, guards, all in bike weight about 35lbs
If I had run the Xcheck with Marathon Supremes instead of M+, about half the weight, I reckon the difference would have been less than 1mph. Though I'm sure I had to work harder on the Xcheck for the 16.5mph than for the 18mph on the Giant, I found I preferred the Xcheck as I didn't feel as battered at the end of the week, and I think that was mainly due to the suspension effect of the bigger tyres. Since trying the Supremes I now wouldn't go back to the M+ unless I had a ridiculously glass/thorn strewn commute.
Lastly, if you're trying to decide between specs then I'd opt for the best frame option, if you get a good enough frame then you can always upgrade the bits as they wear out, especially if it's something with a lifetime warranty.