+1, Gary! Haven't used them myself, but those EX500 carbs show a whole generation of advancement past the older BS series, and this board has developed a deep data pool on them.
OK, funky, you want more options from other makers? Here ya go.
1. Keihin CR series: old style round slide carburetor, tunable for 2 stroke or 4 stroke applications. High price as compared to Mikuni VM, no XS650-specific data.
2. Keihin FCR series: most advanced 4-stroke specific flat slide performance carb made, extremely high end: slides run on rollers, throttle shafts turn on needle bearings, beautiful design. Extremely high price, no XS650-specific data.
3. Dellorto pumpers, as mentioned above. Old round slide design for the price of more advanced Mikuni flat slide 4-stroke pumpers. No XS650-specific data.
There are other options. I use a pair of Mikuni TM36/68 4-stroke flat slide pumpers, and for guys who have the skill and can find them, setting up a pair of Mikuni RS carbs taken from a bank of 4 is also an option. There are threads on this with good baselines, just run a search.