mate you sound like me, I thought I was the only one worrying about dogs hearing. Btw what are the thermal binos you have, they sound interesting?
Some of my own searches on .450-.452 compatible bullets
250 grain gold dot, (normally from the 45 colt)
700-780fps, .67-.80 expansion, 13" penetration
https://www.youtube.com/watch?v=p04Mggfnj00
230 grain gold dots(45 auto)
775fps, .64 cal, 11.75" penetration
https://www.youtube.com/watch?v=4lV8wwCzsso
834 fps, .69 expansion, 14" penetration
https://www.youtube.com/watch?v=8289VCd5pmg
864fps, 70 cal expansion
https://www.youtube.com/watch?v=frFfF-hWpxk
The 230's can be driven over the 1000fps mark and stay together.
200 grain gold dot( slightly tougher bullet than the above)
1064fps, 78cal expansion , 13" penetration
https://www.youtube.com/watch?v=mftGL4VY8QQ
230 grain hornady XTP(tougher bullets)
896 fps, .657 expansion 15" penetration.
200 grain hornady XTP
1011fps, .65 expansion, 17.5" penetration
https://www.youtube.com/watch?v=Pl_anGfqnAI
You'll note with handgun bullets , sometimes they will increase jacket thickness in the lighter bullets to handle the increased velocities. They can all be driven faster than the above, thats just the levels the handguns could handle.
I had difficulty finding much data on 300 grain JHP at subsonic. The 45 colt (using +P ruger loads or lever guns) and 454 casull users on big US forums would have info as they would experiment across the velocity scale.