Hi. I'd just like to make a point here, first. While many people assume that going higher voltage means still using the same resistance that one did at the lower voltage, not everyone does that. I personally like to be able to get the more widely available 'standard resistance' atties and be able to get a warmer vape out of them at 5v.
As it is these days, lower resistance cartos are quite commonly available, so at this point the potential wattage one can achieve with HV devices is getting out-of-hand, IMO. I'm pretty sure I read someone saying something about using a 1.25 ohm carto on a homemade 7v device, somewhere. Besides feeling sorry for the DIY battery unit's pain, I couldn't get the image of this guy vaping a 40 watt lightbulb modded into a clearomizer out of my head...
Anyway, my experience goes up to 12.5 watts (2 ohm @ 5v). Personally, I thought at made my VG liquid take on an acrid property that I didn't like, as if every hit were a partial dry hit. I ended up taking shorter hits, and it was ok. I can't vape PG liquids, so I can't say how they fare at hotter temps, but I can say that VG will definitely point out any potential wicking flaws that you may have, at higher wattage.
I like 1.7 to 2.8 ohms at 3.7v, and I pretty much stick with 3 ohms at 5v, which is about the same as 1.7 @ 3.7v. Most of the time, I find myself using 2.4 ohms at 3.7v, though. I'm not really into having much throat hit, though.
My main draw to the 5v device is the fact that I can get a warmer vape without sacrificing battery life:
3 ohms @ 5v = 8.33 watts, running 1.67 amps of current from the battery.
1.69 ohms @ 3.75v = 8.32 watts, running 2.22 amps of current from the battery.
Same vape at only 75% of the current drain, and I like my vapes from 5.5 to 8.5 watts, I guess, so it's a win.
For my money, I'd probably go with a variable voltage. You can buy any carto, and make it work nicely by dialing it in...