i have a 1997 800 intruder and they are very comparable in size to the 1400.
I'm a big guy, 6'2 -250lbs and if you are looking to keep this bike for a long time, and are looking for comfort, i'd look elsewhere. Don't get me wrong, they are great bikes and are extremely dependable, and i am a HUGE fan of the shaft drives, but they just aren't extremely comfortable for big/tall guys on long trips (as for the highway pegs). If you put your feet on the highway pegs, your knees are up almost to the handlebars.
I drive mine all the time around town (back and forth to school and work) and even on 80+ trips one way every other weekend and during the 80 mile one way trips, after about 30-40 miles, i am moving my legs around constantly becuase the highway pegs are not comfortable. I usually rest my legs (calves) on the pegs and that is as close to comfort as i can get. I don't mind the upright position with your feet right under you, but after a while, you'll want a larger, more comfortable bike.
I have yet to find a seat that moves you back any on the bike, which in turn, would allow you to stretch your legs out more.
The differences, that i have read, is that the 1400 is better on the highway, as the fifth gear is higher, so it turns less RPMs and lets you cruise more comfortably. My 800 rather, has a lot more pick up from stop, but has all lower gears, and turns higher RPMs on the highway, but i cruise at 70-75 no problem.
I personally like the look of the thin cruiser, but if you want a lot of comfort, look at the 1500, if you want a thin highway cruiser, go 1400, if you want thin and pickup around town, go with the 800.
sorry for the rant,