I am getting ready to get some new tires with a 10.5" width, and also going to be lifting my Ex 2 more inches. Right now I have a 4" suspension and a 3" body with 33x12.5 tires. Going in is a 6" suspension and probably 34x10.5 tires. My question is do you guys think that 3.75" backspacing would be sufficient with a skinnier tire and taller ride height?

3.75" will be fine. Stupid question: why go so skinny? The X will feel much tippier and will handle worse. You also have a greater rollover risk. The only reason I see for skinnier tires is if you do a lot of mud and want to sink down and ride the bottom of the mud pit.

The tires in particular are the Swamper LTBS. The first reason they caught my eye is their price. I had posted another thread asking opinions on them and had gotten good feedback on them. The rollover risk was the main reason I was asking about the backspacing, because I knew there would be greater risk going from 12.5 to 10.5, but was curious if going with less backspacing than 3.75 would be worth it, or if 3.75 would be fine. As far as mud, I do not do a whole lot of it if I do not have to. And from what I have heard they do great on the trail.

I'd get wider tires, but that's just me.