IMR Blue is discontinued. Based on your stated uses, I would work up a mild to moderate 44 load with it and just use it up.
Quickload says Longshot will do ok in 10 mm. You will lose 20 fps or so for a 180 and 50 fps or so for a 165 in comparison to Blue Dot.
If you want more from the 10mm, Quickload says to be on the lookout for
- Accurate: TCM, #7 or #9
- Shooters World: Major Pistol, Heavy Pistol
- Alliant: Power Pistol
FYI, I started using Heavy Pistol a few years back after have issues with some other powders. It is very close to 2400 in burn rate, meters great and is not finicky at all. Unlike some magnum pistol powders the maker says it is ok to reduce loads with it. Cost is about as reasonable as any.
