I know the thread is quite old. nevertheless I can share some results for anybody seeking the information.
I am using 13,6grs of N32C, standard primer and 220 GRS Hornady RN3090 bullet. OAL 3,210". Barrel length 22", twist 1:10, v2 is around 310m/s
Depends of your barrel twist but with a 1:8 barrel you could use those 208/225 VLDs style bullets like the hornady 225 BTHP and because the round is so long it'll help with the fill rate.
Trail boss would be a much better, safer powder than Tinstar for that. I use tinstar for heavy 308 subs (240) but trailboss gives me a much better case fill on the 200-225gr which translate in lower SD/ES
For 30-06 subsonic 225 BTHP with Trail boss you could start at 13.0gr (75% fill) and work your way down to 11.5gr (67%)
with Tin star - 13 gr is 50% fill and 11.5 is 45% - starts to get pretty low for comfort - plus the ES will be shit, especially if you shoot upward or downward.
with 208 eld-m for example @ 3.30 coal - 13gr gives you 75% fill and 11.5 67%
One of my favorite subsonic 30 cal bullet is the Lapua 200 FMJ-BT and should stabilize in most 1:10 twist barrel but then again work down the load - make sure it doesn't keyhole and get a good chrony when working subsonic loads or that's a recipe for something bad to happen.