Unique is "dirty" at low pressures, but cleans up nicely at higher pressures. Unfortunately, 38 and even 38+p is a low pressure round. 38 special loads are about 12,000 psi at max and Unique is just barely getting happy at this pressure with lots of soot and unburned flakes.
I shoot the Lee 358-158-RF seated to .355" with 5.0g Uniuqe and the powder is pretty happy at that load which gives me about 990 fps through a 4" Ruger Service Six.
With your 750 fps loads, you'd be much happier with Clays. I load 3.0g and with my bullet, I get 750 fps and a real light recoil. If you seat your bullets shallower, you might need to bump the charge up a couple tenths. The powder burns completely and generates lots of pressure for consistent veolcities, but you don't want to squeeze any more velocity out of this powder or you'll be over pressure quickly.
If you want more velocity and a clean burn, get some Hodgdon Universal Clays aka Universal. It is based on Clays technology and is a slower powder which performs like Unique, just cleaner and more expensive. International Clays is between Clays and Universal (sort of like Green Dot being between Red Dot and Unique).
I love the economy of Bullseye, but it will turn a stainless revolver into what looks like a blued revolver in 50 rounds.