OK, I know this is the most asked question in the world but I'm gonna ask anyway since everyone is a little different.
The background: I'm 52, 5'11" 180# and started on a Honda 90 when I was 14. Rode small (<250cc) bikes for about 15 years but have been off up until this weekend. A friend has a bike and broken leg which don't mix so I'm keeping his bike from getting rusty. It's great for getting the feel again ( Suzuki GS550L )and I have my wife agreeing to getting back in the saddle. She is 5'10" and we will need something that will ride 2 up comfortably for mostly short trips, less than 200 miles one way, though I would not rule out the possibility of a longer trip on occasion. Looking at the 800-900 class but am open to suggestions, don't want to go over 1100. Brand is also an option, but $$$ is certainly important.
Thanks in advance
Gomez  

You probably can get away with the 800-900cc range. Your problem may be your wife.
She's 5'10", which probably means longer than average legs. You may need to look around for adjustable footboards. I've only seen them once on the internet, but they do exist, My wife is 5'4, so, I never pursued them. Ok, I did eventually get a bigger bike, because she wasn't willing to do more than about 200 mi in a day on the back of mine.

When she's on hers, its not a problem. (hint... hint)  

Thanks frbock, that will certainly be a consideration, both the distance to the pegs and getting her own.
Also think maybe I should ask my questions instead of leaving it so vague.
#1: From what I have read here, I'm guessing that 750cc will not keep me happy and I don't want to be trading up next year. But will 800 work, is 900 better or should I jump to 1100? Both the C50 and Vulcans get good reviews and those are my primary interest right now.
#2: For those of you who carry a passenger, is there a comfortable factory seat? I don't want to shell out $400 for a Mustang right off the bat.
#3: I'm thinking fuel injected, cast wheels, belt or shaft drive.
#4: There doesn't seem to be a lot of price difference between new and late model bikes, but I have also seen several used that already have windshields, after-market seats, etc. instead of buying them on top of the price of new. So far all of our looking has been online but we are talking about hitting some dealerships this weekend.
Hope this makes it clearer than bugs on a windshield.
gomez  

HI; I have a 05 C50T.  I don't normally ride 2 up. When I do The bike handles great. It is still very responsive and stable. I have not had any trouble running 70+. I just did today. A friend just bought a 08 Yamaha 1100. Very nice bike. He really did not like having to ride in back.  He did say that it was not as bad as he thought it would be. I am 5,10 190 he is 5,5 150 and my bags are full along with back pack. I had close to 370 lbs. and ran great. I think that any bike with 800-1100 cc would be good. They all weight close to the same.
2  The seat on the C50T is good for me. It has plenty of room to move around when needed. I can ride about 1 1/2 hrs before I get TB I can go 2. By that time you will be ready to get off any way. Just to streach your legs. Get a drink or something..
3 Get the bike with fuel injection. I get 49-50mph. I like the shaft dr. It is smooth doesn't make noise. No adjustment or maintaince. Or very little check the gear oil once and while. The reason my choice for the shaft dr. is that I live in a very sandy area.   The wind blows it eveywhere. Chains and Belts just don't seem to last very long.
4 I should think  that you should be able to get a good used bike with all the stuff you want on it for less $$$ than new. IF your area is any thing like mine there are a lot of bikes up for sale . Guys buy them and find out that they really don't like the whole bike thing. I have 2 at work that bought new and are just teriffied of riding. One only has 11 miles on the bike and won't get back on..The bike is 2 years old now.  
Take your time test ride as many as you can. Let the wife set on back just to see if she fits ok.Some times the pass just does't fit on the back very well  then you have  problems
There tons of foot boards and adaptors in the marketplace so you should be able to get the pass comffy and don't for get you need to get comffy too..
scruffy... GOOD LUCK....  

You need look no further than the Kawasaki Vulcan 900, my friend   It will handle two up with no trouble for the type of riding you described.  I have 2500 miles on mine and use it for daily transportation to/from work and joy-riding on weekends.  As for a seat, you needn't get a Mustang, but your wife will probably appreciate a swap from the stock unit.  I have the Kawasaki Comfort Gel Seat (about $220 from the dealer) that works just fine, thanks.  

The Vulcan 900 is basically my Vulcan 800, with all the flaws fixed. FI, belt drive.

I tweaked my 800 with K&N intake, progressive front and rear, had the carb adjusted, and I did get 37k before I traded it. It still kept up with the big boys, but, it lacked a little on 2 up comfort.