Using a brand name premium gas has completely eliminated the backfiring from my 900LT.
I use 87....(regular). There are still 2 independents in my area that (say they) sell non-Ethanolated gas - although that may go away this September.
Personally - I think a VN900 will run fine on any pump gas - and unless you bolt a turbo, a supercharger, or start huffing giggle gas, you're probably not going to notice any difference between Regular, Premium, Ethanol, or Non - Assuming you don't try to use E85 gas, which is unavailable in my area...
However (comma) there are always folks out there who have machines that run better on Premium - and NOBODY knows a motorcycle better than its operator (usually!)
I had a Mazda Protege once that pinged like CRAZY on non-premium gas (from the factory) and nothing I could do or adjust would change that, and OH how I tried for 250,000 miles!
Since the price delta between 87 and 93 Octane for 5 gallons of gas is only about a buck or so - I'd say burn whatever the heck you want to! Just don't let someone get away with telling you that you HAVE to. The VN900's compression ratio is pretty low - about 9.5:1 - which is well within the "regular pump gas" range for most motors.