How do you find the 1700 compared to the 900? I have a 900 as well and I am thinking of selling it and buying the 1700. But I still have doubts.
I drove a 900 Custom for 10 years before buying my 1700 Vaquero in 2017. Here's my take:
Size: The biggest difference is size seems to be seat height. I have a 33" inseam and I have trouble flat footing this bike. On the 900 I could flat foot with my knees still bent. Both bikes have the Mustang Wide Vintage Touring seat and although I can't measure it, it feels like 3 or 4 inch difference. Both bikes are roomy, but I liked the foot position on the Custom better. Well, it took getting used to on the Vaq.
Weight: The Vaq is about 200 lbs heavier than the 900, but I mostly feel it when I'm pulling it up off the side stand. On the road it doesn't feel that heavy. That said, I have to be careful where I park. Pushing 800+ lbs around a parking spot can take some effort. Backing up a grade is really tough, especially if there's loose sand or gravel on the road.
Ride: The extra 200 lbs along with air adjustable shocks makes for a smoother ride, in particular at highway speeds. Unlike others, I find that the large fairing causes more issues with air wash and cross winds. I road my 900 with a windshield and later with a Memphis Bat Wing. I get pushed side to side more on the Vaq than I did on the 900, but that was a Custom so maybe the fork's rake had something to do with that.
Performance: NOTE: both bike are mechanically bone stock. The only aftermarket accessories were for style and comfort. I found the 900 to be quicker off the line, although that may be me being hesitant to open up the throttle in first gear. I'm not a tire smoker! I found the 900 to have decent acceleration up to about 75, then you could coax her up to 105 but you didn't get there in a flash. The Vaq's 6 speed transmission took some getting used to. 5th and 6th are both over-drive. It takes some discipline to stop shifting into 6th below 60 mph. If you try to use 6th gear around town, you'll never stop shifting. Up, down, up, down. I have to force myself to stay in 5th. Above 60 you can stay in 6th gear all day long unless you want to smoke somebody or climb a steep grade with a passenger.
But on the highway, wow!. I was on US 15 in Pennsylvania last year and I pulled out to pass a tanker. I was doing 75 in 6th gear. I didn't downshift, I just pulled out and rolled on the throttle. I glanced at the speedo as I pulled back into my lane and I was doing 115 and the needle was still sweeping to the right! I never felt it. The ride was that smooth and the air around me so still I thought I was doing maybe 90.
Mileage and Range: The 900 is all over this one. Over the 45k miles I put on my Custom I got between 48 and 52 mpg (indicated). With a 5.2 gal tank that's 250 miles before you have to get off and push. The furthest I ever took it was 252 miles and the pump said I put in 5.3 gallons. The Vaq has the same size tank, but I'm lucky if I get 40 mpg. I've stopped checking but the last couple of tanks I checked I was in 38 range. When I planned my trip to Baltimore last year I mapped out gas stops at 175 mile intervals but I don't think I've ever had to put more than 4 gallons in at once. Also, the 900 loves 87 Octane. I don't know why (both bikes run at the same compression and temp) but the Vaq requires 90+ and seems to run best and get the best mileage on 93 Octane I get at Kwikfill.
I really wish could afford 2 bikes. I love my Vaquero, but I do miss the 900. There were a lot of things to love about that bike, but Hell, I kept it in the family. My son owns it now.
Good luck and let us know what you decide to do.