If I can get my snub nose J frame to push a lead 158gr to 800fps with 4grs of fast powder.........

You should not have any problems with titegroup and your 4" barrel getting a 850 to 900fps load and still reach a safe chamber pressure.

As a note, my 6" 686 shoots little holes in targets with the 158gr Lwc only doing 755fps.
Kills paper but a little light for steel use.

850-900 might be doable for steel but with your weapon you
should be able to get up to 950fps if needed with other powders.