If you handload, .38Super +P, 9mm +P and .357mag brass cost about the same. You can order brass directly from Starline and they pay the shipping costs.
VihtaVuori #4 manual has extensive data for the .38 Super, including loads that take 124gr JHPs into the 1500fps range and keeps chamber pressures under 34,000 psi.
I've experimented with the .357cal, 125gr XTP in .38Super, this recovered 125gr XTP had an MV of 1491fps from a Colt M1911, ejected brass was from 5ft to 6ft;
The 125gr XTP is designed for .357mag velocities that the Super can match at relatively low operating pressures. I don't know how the single action trigger pull is in your Witness, but from a 1911, cold split times on target are faster than my G17. By cold I mean bare hands during winter time, well, in Arizona what passes for winter temps is different than I was used to.
If you handload, this is what you can achieve;
Not only was that dried out range cow leg bone very tough, but the XTP bullet first penetrated a 14 ply semi-truck tire casing before hitting the bone.
So, how tough are these bones to pentrate? This .40 S&W 180gr bonded PDX bullet ripped open on a much thinner, flat bone;
For me in my very rural living environment, the .38 Super is a working carry caliber that's been very effective on 4 legged vermin.
Enjoy!
Bob