I had a Wesley made for me with carbon on the back (68 inches, 58#)and didn't particularly like it. Ordered another at the same weight but two inches shorter (Actually a Big 5, 66 inches,and came out at 60#). Really like the latter. To me, the glass bow draws smoother and it feels faster. Of course, it's a couple of pounds heavier than the Wesley. The short of it is that I couldn't tell if the carbon added to the bow's performance.
Don't know whether the difference in feel/stiffness is due to the carbon backing or the extra lamination or both. Craig will tell you that the more laminations (and glue joints), the more limb memory. Limb memory is another term for stiffness. But that stiffness doesn't necessarily translate into performance. For me, I've decided that I don't want 5 laminations in my limbs. That's why I now shoot Big 5s, and if the right Tembo comes along, I'll be snapping it up.
Probably not a lot of help to you, but for what it's worth, I honestly couldn't tell that a carbon back added anything to the bow's performance, and in fact, it made the bow feel stiffer on the draw to me. On the other hand, $75 (the extra cost for a carbon backing) isn't a pile of money, and you may want to give it a try to decide for yourself. Good luck.