My last one was the XS307 -- the 15 liter. I was *very* happy with it on the bike it was on. The Versys seems to have a more sloped tank, so I'm going with the XS308 this time -- the 20 litre referenced above, which seems to be more form fitting.
Great bags... no vibes, no shake, solid connection, easy on and off -- nice system.
My only nit with these bags are the new "waterproof" close-able liners... they're useless, and take up room (which is at a premium in tank bags). Might just cut mine out.
2015 Versys 650 Pearl White
[space holder for farkles...]