Having tried Rip Curl 4/3 Dawn Patrol and Feral 5/4, I can say that Xcel Comp X is definitely warmer and have more shoulder mobility than Rip Curl base model, as it should at double the price. It has all the nice premium features like seals around the feet/arms to prevent water ingress, softer neoprene, and magnetic latch (this is a pretty nice bell and whistle).
At time of review, I've surfed 3 times in this suit. Xcel fuzzy liner is comparable in warmth to my Feral 5/4 (at 4.5/3.5 thickness) and similar in shoulder mobility. I surf in chilly NorCal waters. However, it is slower to dry than the Feral, so there's the tradeoff.
This is a good purchase for me as someone who has multiple suits for consecutive day surfing.
As far as fit goes, I am 5'3 and about 132lb and purchased an 8 and it fits true-to-size (8S would be better for me but they didn't have my size and 8 still works.)