I find that Unique "cleans up" pretty well, when it is used in loads that generate 20k psi or more. The application of slightly more taper crimp helps matters, also. If one simply cannot get past the "dirty burn" of Unique, there is Alliant BE-86, which acts (for me at least) like a cleaner-burning, better-metering, flash-suppressed version of Unique. Reloading data for the two are not EXACTLY interchangeable, but the variance usually stays in the 2-5% range. Given the current troubles finding suitable propellants, one may find it easier to locate BE-86 than Unique, for the near future.
I also concur with SEMPERFIRELOADING on his recommended load data for Hornady 125 gr. XTP projectile and Alliant Unique. I use 5.8/Unique/125 gr. FP-PC, and get closer to 1275 f/s, but it is likely due to the higher lubricity of the polymer coating.