Most of my loads for .40 are to meet 165 PF with a 180 gr. bullet for IDPA & other local leagues.
Am using both WST & Titegroup. TG is somewhat "snappy" compared to WST but
it's a whole lot cleaner than WST.
If you want a med. recoil load with a 155 consider trying Titegroup and -10%
of Hodgdon's max listed on their site.
Sierra's Manual lists 6.9 of Unique with a 150 gr. JHP running at 1,100 fps.
Their lowest loaded listing is 5.6 gr for 900 fps with same bullet.
5.9 = 950; 6.2 = 1,000 & 6.6 = 1,050 fps. So 6.8 is far from a "med. load".
These are all from a 5" bbl. You did not mention if you were using plated or jkt'd. bullets so if plated should reduce anywhere from 2/10's to 5/10's gr.
All that said I agree with Greg:
"You can't go wrong with Titegroup." It's clean, inexpensive, meters great,
isposition insensitive and has very consistent vel. even with light loads.