I've got my 8-wt Xi2 paired with Sharkskin (same weight). It shoots a fair stretch (for me), unfurls well, and floats like a charm, but has all the same problems discussed in other forums on this site (e.g. noise, tough to clean, absurd price, etc). On big strip sets (a rarity) it digs canyons in my fingers. Don't get Sharkskin if you've got a blood clotting disorder.
I've used a 6 wt Xi2 regularly for the last couple of years with the 6 wt Outbounds, which are around 1/2 a wt heavier than standards. I just replaced the 6's with 7 weight lines, and wish I'd done so years ago. It works superbly.
That doesn't mean it's necessarily true for the 8wt though. Each model is different, and you and I probably cast differently. Go to your favorite shop where they will let you (and probably help you) actually cast, and decide for yourself.
The old Rio running lines in intermediate and floating have a well deserved reputation for tangling. The new Outbound Short (30' head) and the intermediate running lines found on the sinking lines are fine though.
OK. I lawn casted the Outbound in an 8 and it performed very well. It's a keeper. The thin running line will take some getting used to. Casted best starting with all 37' out of the guides and ample running line at my side.
The Outbound always casts best with the entire weighted tip out. That loads the rod properly. You don't have to overline the Xi2. I have a 10 wt. with a 10 wt Outbound and it casts beautifully. I demoed a 7 wt with both 7 wt Outbound and 40+. They both casted well.