I have a B650 and now a 2008 GW 1800. Have owed GW's 1500, 1200 and 1100. The B650 allows you to be a little sloppy when driving really slow because of the weight. I can look around a bit when coming to a stop. The GW will require more attention. You need to more closely judge your speed, placement of your feet ect. The GW footpegs can catch the back of your leg when coming to a stop or taking off. You will have to learn to downshift when coming to a stop. With time it will come more natural. I can drive the B650 at slow turns with the front wheel nearly locked completely to the right or left. I can't do that with the GW.
On this board, some people mention lightly holding the brake on the burgy, and speeding up the engine slightly while making tight turns. I does help on both the burgy and GW. On the GW, you can do the same technique but use instead, ride the clutch a bit while speeding up the engine. Easier to do on the Burgy than the wing because riding the clutch requires a little more finesse.
I can go back and forth between the bikes with no problems running the brakes/clutch. You use the front brake more than the rear and that makes it simpler. Front brake is still on the right. I feel my GW sits a little lower than the B650. However, that may be because of the feet position. On the GW my feet are in more straight down postion. On the B650 thay have to placed a little wider. The pegs of my GW also sit a little lower than the floorboards of the Burg 650. I have to raise my feet/legs higher when taking off on the Burgy.
Biggest mistake I make on the B650, is not manually shutting off the turn signals. Can be a huge safety issue on the B650. I have become extremely use to having bikes with self-canceling turn signals. It should be standard on the newer B650 executive models. Wake up Suzuki. Much rather have self canceling turn signals than motorized folding mirrors.
For the most part, dont worry about riding slow and overheating with the 1500. Not an issue. Some of the very early years of the 1800 GW series had heating issues at slow speeds. Was a combination of some bad castings in the engine or the radiator fan at slow speeds. (At slow speeds and when stopped, the 1800 GW fan blows forward rather than back like most fans. Thus when traveling slow, the air being pushed forward by the fan, was matching air being pushed back by traveling forward- not good cooling thru the radiator.) Harley guys hate riding slow or stopping on hot days because their engines are oil cooled and can overheat. You won't have any issues on the GW 1500.
The 2 biggest things I notice. 1. The GW is quieter-especially at speed. Both wind buffeting and engine. 2. GW is really smooth over the road surface. The GW 1500 is suppose to be slightly more plush than the 1800.
The 1500 does have nose dive issues when braking. That was corrected with an anti-dive valve in the forks of the 1800. The dive is not dangerous IMHO, but will pitch the front of the bike and you down when braking hard. I don't notice that as much with the B650.
I bought my 2006 B650 a few months ago. Had planned on replacing the GW. The B650 is fun to drive on the shorter distances, easier to drive in parking lots, and just easier all around at the slower speeds. However, on the road or at distance, the GW is far better. My GW has the creature comforts- radio with great speakers, GPS, intercom, smoother ride, backrest for driver and passenger, better seats, better windshield ect. More storage for traveling on the GW. However, the higher price tag of the GW allows for many of these comforts. I bought the B650 used, fairly cheap and will probably be selling it this month. I don't need two bikes. I will miss the automatic transmission of the B650. Many people want that put on the GW.