I too use UPP as a topper over AIOx2, SGx2 and am soooo happy with the results on Alpine White III.
Beading is great and it does last. I got 4 months of protection during a typical Iowa winter. Wash every two weeks and touched up with ultimate gloss enhancer. Beading and slickness was weak at 4 months but not gone. Overall gloss was very good at the end.