Hi Korgasm,
Stick with the XV IMHO. I own a JV-2080 and, yes the midi timing is terrible. I didn't notice it while playing it one sound at a time. However, in a sequence, the timing is bad. If I hadn't sold my old modules to buy it, I would have returned it and stuck with my old kit. However, they were long gone and now I'm stuck with it until I can buy something else. I have too many gigs right now that I cannot live without at least this sound source.
If you like the sound of these units, then the XV is probably better. When you get it home, check the timing on it. You may want to check it against the store's JV-2080 as well. Take some percussive sounds on different midi channels in performance mode. Trigger them at exactly the same time on a sequencer. The more sounds you use the greater the timing differences will be. Don't worry about some of the timings you'll hear. MIDI, by its nature, will have noticeable timing differences between notes going to a single MIDI port. However, hopefully, the XV's have a faster processor in them to trigger more reliably.
In regards to my setup (in case you're interested), I'm looking into a few options right now (some being more expensive) and, when I've decided, then I'll get rid of it. I am not interested in the XV's though. I like some of the sounds in the JV and it gives a ton to select from. However, the sounds aren't the greatest and I think that before buying something else now, I will wait until I really like the sounds of my next module/keyboard.
HTH,
Fernando