Calibre Bossnut Rear Tyre and size

Why would you want anything bigger than a 2.5 tyre on a full susser, besides what's written on the sidewalls is not what you get. The frame you have is designed for a max tyre of 2.35, the forks are a different kettle of fish, also remember as the tyre widens the depth increases.

The problem with the Bossnut is the clearance to the seat tube. Take all the air out of the shock and compress it all the way. The rear wheel on my v1 was close to touching the seat tube with a 2.25 Nobby Nic doing that test.

The WTB vigilante is not a tyre you would normally put on the back wheel, faster and narrower tyres for the back, wider and grippier tyres on the front.

A 2.4 is plenty big enough on the rear, on your bike in some brands that may be too big, Schwalbe tyres come up on the large side, my Magic Mary 2.35 at 62mm is as big as some 2.6 tyres, so as previous posts care must be taken.

There are several reasons why I would not put a tyre that size on the rear of your bike.

#1 It is important to get the grip balanced front to rear. Ideally you need more grip on the front so that when cornering hard the rear lets go first.
#2 Having a faster rolling tyre on the rear helps to reduce drag on those long climbs that happen from time to time.
#3 What is the internal width of the rim on the rear wheel? For a 2.8" (71mm) tyre the internal rim width needs to be at least 30mm so that they tyre has a decent shape and doesn't look like a balloon. The shape has to be good otherwise the tread is not properly presented to the trail and you won't get the grip you are expecting. Also, the tyre beads will not be properly secured to the rim, which risks the tyre coming off the rim if you are pushing hard. See the link to the Schwalbe tyre knowledge sight, click on "which tyre fits which rim", look down the left to 70 and across to your rim width to see if it fits.
https://www.schwalbe.com/en/reifenmasse.html
#4 You need room between the tyre and the frame. The frame flexes, the wheel flexes, the tyre carries mud and grit. The last thing you want is for the tyre and the frame to contact each other. Don't forget how close the wheel can come to the seat tube when the shock fully compresses, let the air out of the shock to check.

If you want to use a tyre that size on your bike, you would be far better fitting it to the front wheel, provided if will fit under the fork brace and reasons #3 and #4 above.

Ask yourself why you need more grip on the back? Is your rear wheel spinning out when climbing out of holes or up steep hills? If so, you can increase grip by changing the tyre for one of the same size but with a better tread pattern or one with a softer compound. But be careful about #1 and #2 above.

You can't put 60psi in a 2.5 tyre it would be well over it's limit. Tyre sizes are normally measured at 25psi.

The Bee Line is a tyre for conditions we don't have at the moment, plus you're running too much air for mud, 27-29psi is probably enough for your weight, 2-3psi less in the front.

The size of the tyre won't change with pressure, fat tyres do not work better in mud, and your tyre pressures look way too high.