In the drag strip real world testing, there is no difference in power. Because your above the point of the vboost opening 98% time. Your only out of the vboost at launch, which your at 4200 rpm at launch ( at least you should be ). So the actual power difference is nothing.
Basically what your doing is letting two carbs become one and over carb the motor at low rpm.
Running no vboost setup on a stock bike with no aftermarket mods will decrease performance down low in around town city driving.
If the factory found that vboost was beneficial at lower rpm's then would have lowered the opening point.
Adding aftermarket components to the mix then changes things and having it open all the time can be benecifical. But in my personal testing on several bikes, it made no difference other than sound cool and needing to be tuned differently to run better.
My first Vmax I didn't touch the Vboost, but on the next 5 I tried them all in various states and even though I had stage 7 carbs and Dale Walker exhaust on my fastest bike ( 10.80's ) I found it more beneficial to run it with the Vboost operational at the factory setting.
The idea is that the volumetric efficiency and valve timing at rpm levels set at the factory, the factory found the setting that they can achieve proper atomization and function without overwhelming the proper function of the carb. If you open the v boost too soon without properly supporting the change in cv function of the needle position you'll throw it out of whack.
I am sure Dannymax might be able to explain it better than I can since he is a carb guru. Sean Morely if I recall correctly pretty much says the same thing, stock seems best.
There was a post going a few years ago. Many notable members commenting on the idea there. FYI.
http://www.vmaxforum.net/showthread.php?t=23503
The consensus is it feels faster, but reality and dyno shows its not. Obviously everyones bike is different. I ve tested it enough on my past bikes to not bother with it. If you want to run without vboost, go flat slides!