I have a pre-SE XL in .177 and refurb XL SE GRTs in .22 and .25. They all shoot excellent. Those barrels are no joke.
I found the UK XL locally from a Craigslist ad for "hunting items." Both front stock screws were broken, but I was able to extract and replace them with no problems. I polished and lubed the spring ends and put in a piston sleeve to detwang everything, but I did not venture to remove the scope rail and piston. Didn't need to, it shoots extremely consistent right around 12fpe. I also polished the trigger surfaces and maybe installed a lighter return spring. It's a keeper.
I just grabbed the .22 GRT refurb from field supply for obscenely cheap, but it arrived with a deep crack in the stock wrist area. I contacted BSA US, and they say they can't get a replacement stock, but would see what they can do if I send it in. I think I'll just repair it. I test shot it despite the crack, and it insisted on stacking pretty much any pellet I put through it. It makes around 15FPE. The trigger can be improved a lot with some polishing and a longer M2.5 adjustment screw, but don't go too far, because the screw removes overlap.
I like the .22 so much, I took advantage of an Ebay coupon and picked up a .25 refurb at a reasonable price. It shoots very well with FTT and GTO pellets, hitting almost 17FPE with the GTOs at 680fps and the FTTs at 595. The stock on this one is not broken!
I'm sort of a fan of the BSA SE springer platforms since they can be found fairly cheap, aren't too terrible to work on, and come with great barrels. I have a pair of Supersport SE springers in .22, both soft tuned to 12 and 13 fpe. The Lightning SEs with their shorter barrel and heftier stock seem easier for me to shoot accurately than the longer barreled Supersports or the lighter 1st gen XL. I will warn you though, that after many thousands of shots, I am getting some pivot sideplay and horizontal group spread in one of my Supersport SEs. I'll try to shim the pivot one of these days...
Here's a comparison pic of the original XL and the .22 GRT SE, and a pic of the .25 GRT. The .22 serial number ends in -15 and the .25 in -13 so, I assume they are 2015 and 2013 models. Also a family pic with a UK Supersport and Supersport SE for comparison.
Thanks for asking and have fun!
.