You can explore how your 900 will perform in different combinations using the tool at gearingcommander.com. Choose the Vulcan 900. The tables give you performance for stock pulleys, which have 32 teeth (front) and 66 teeth (back), and the stock tire, a 180/70/15. You can reconfigure the front pulley, back pulley, and tire size to see how speed changes at a given RPM.
The Baron front pulley has 34 teeth, so type that into the "Current" line, replacing the 32, which is also in the "Stock" line. Look at the effects by clicking "Current", clicking back to "Stock," etc., above the table. To compare this change with adding a 200/70/15 tire instead the front pulley, put that tire into the "Custom" line. Click between it and the "Current" line, and you'll see that adding this rear tire has about 2/3rs the effect of adding the front pulley.
You can do the same thing with Baron rear pulley, which has 62 teeth (instead of 64), with different tires, and with all combinations thereof.
Personally, I did the front and rear pulleys on mine before reaching the need to replace the rear tire. I am very happy with the two-pulley mod. You do lose a little snap off the line, but after that, I find that everything is better, especially RPMs when cruising above 55, which is roughly about the cruise speed that determines whether use 4th (below 55) or 5th (above 55) now. I like cruising in the city better. Rumbling through a town at 25-30 in 3rd occurs at somewhat lower RPM, which is nice, there is enough there to handle a hill or the need to get up and go. 4th is now a nice 35-45 through town gear. I used to be in 5th at those speeds, even in the mid 30s if there weren't any hills. No longer. Fifth is now strictly a highway cruising gear. I wouldn't really call it an overdrive. I would call it a nice highway cruise gear, and if it were me, I'd have geared the bike this way from the start (well, maybe I'd have added a 6th to the stock gearing). That's just me. Others may disagree. Get a feel for your bike. You can play around with gearing commander to get some sense how the different feel in terms of vibes you get after the mods.
There negatives to the pulley mods, at least that I've experienced (your mileage may vary). My rear Barron pulley is not quite true (it's just a little warped), and that might be why the belt makes more noise than it did before I changed it out. I'm not sure. I'm watching belt and pulley wear carefully. No pulley is "perfect," so I can't say a lot about how much it's out compared to the stock pulley or others, but the shop that installed it pointed the warp out to me. They said it was "pretty small," but might raises issues, they couldn't say for sure. I do hear a very slight "wa wa wa wa wa" at around 40 mph in 4th and have wondered whether that might be due to pulley imperfections. Who knows. I chose not to send it back and am just watching belt wear carefully. We'll see how it goes. So far, I'm managing the noise with occasional belt cleanings and a bit of dry silicone. Some say that causes the belt to attract dirt and is bad for that reason, but I am not finding that what I've been using causes the belt to get any dirtier than it did before.
It's all a journey, isn't it?
Happy and safe riding,
Dan