I've owned two Vulcans...a Gen 1, and now a Gen 2, both in .25 caliber. Quality has improved with each generation because the owner listens to his buyers. Service is next to perfect. He answers his emails and deals with customers personally.
If you are looking for a one hole group at 50 yards, the Mutant and the Vulcan can both provide that. The Mutant should be out in .25 in 2017, but the exact date is unknown.
The Biathlon side cock lever is offered as an option by Vulcan now as a $120 option, it's well built and I have one ordered. If you can operate a torx screw driver, without fatal injury to yourself, it can be easily installed by the gun owner. I suspect it might be a standard feature in 2017...if it isn't, it should be. Smooth as butter!
IF you decide on a Mutant, I've owned that one too, and want max power, get the Standard length in .25 caliber. The Shorty is a great gun, but you won't be dropping any elephants with it. The Standard has that longer barrel you desire for max power. The Vulcan comes equipped with one size barrel sufficient to get the job done.
The Vulcan .25 is about a 45-50 fpe gun. You can push it a bit further, but when you can shoot the eye out of whatever you can steadily hold a crosshair on, 60-70 fpe just costs more air usage, and dead is still dead. ("Deader" is not a word one associates with 60-70 fpe!). Keeping the Vulcan around a 45 fpe gun gets max accuracy, max shot count, and lower muzzle report, especially with the "Colibri Style" baffles in Gen 2 and on...
These are my opinions. Either gun is a hand's down winner for the money. If it just wasn't for that butt-ugly Mutant stock! (I heard iride-Mike carved his own, and it's said to look good!)