Well, for simplicity sake, figure a lot of people find 5v the sweet spot with a stock 510 atty. Looking at the chart, that's 10.87.
So if running 6v then a stock atty = 15.65 (thus the burnt taste).
6v + HV 510 = 8.00 so better than 3.7v but not enough to reach the "sweet spot"?
6v + stock 901 = 9.73
6v + stock 801 = 10.29 (about the same as the 5v+510)
Keep in mind that attys run at higher voltages may not last as long. Also, people tend to prefer one atty type over others.
The chart is really useful to determine what to change in your setup to step up/down per your needs. Say you normally use 510's @ 3.7v and want more TH/vapor, then you could try 6v+901 where as the 6v+501 might be too much.
Obviously, peoples taste are each different so everyone's IDEAL will be different. Just consider what you're used to and using the chart you can see what a change in atty or battery will do.
I've only ever used a 901@3.7v and it's not enough to get me off analogs. But, a stock 510@3.7v might make enough difference for me. If not, I'll need to step up to 5v+ b/c what I'm missing from analogs is the TH and heat (love the flavor of the 901 though!)