I’d echo Lyrikal regarding difficulty – there isn’t any really. A couple of rock gardens in CW that might take you by surprise if you ride the trail blind but other than that, zip. There are however some fairly tight sections with trees and rocks in daft places which can make it a challenge if you are traveling briskly.
If your friends are local and ride bikes then they should know Donard and Tollymore. Far more challenging trails in there (ask them to show you Deer Hunter and Son of Deer hunter in Donard, if you want a challenge) but you’d need to know where to find them. Donard also drains very well so is great to ride in any weather.
Of the new trails i’d suggest Davagh as it’s the most fun but it’s pretty short (20k ish).
p.s. If you like jumps then stay away from the jumpy DH trail in RT. Whoever built it doesn’t appear to ride a bike. The only time in my life that i’ve ever been disappointed riding my bike (and i’m easily pleased).