I have read many posts about one powder being cleaner than another, and Unique certainly deserves its reputation for leaving residue behind, but none of that has ever made any sense to me. I'm going to clean my gun after I am done shooting, and for many guns, they will get cleaned in-between groups, so what's the difference if there is a tiny amount of residue, or a much great amount, to be cleaned out? My bigger concern is always for the copper fouling anyway...the powder residue is something I pay almost no attention to, unless it's blocking the bore. (In which case, something is
seriously wrong with the load I'm using!

)
Actually, I did have that happen once when shooting hot 22LR loads in an old single-shot. All I can figure is the barrel/throat was eroded enough that there wasn't enough pressure build-up for the powder to burn completely. What I wound up with was a nearly plugged barrel, full of partially burned powder. Needless to say, I cleaned it thoroughly and switched to different loads!
I've just found Unique to be very useful over a wide range of applications and if I was limited to only 3 powders, it's one of the three I would certainly keep. Looking at the data for what you're wanting to do, I'm not sure it will go low enough in velocity and still be a safe load. Good luck finding a powder that will.