Building a 1000fps FBI load in 357 brass is a great idea. Should be effective and easy to handle in your gun.

Then you can make some screamers with your 125 JHP’s. Lots of powders can get you there in a 6” gun.

My take: Published data is only foundational. It's intent is to safely get a bullet out of the barrel. Their numbers are their numbers, not yours.
Terminal ballistics are a different subject. Set the load data aside for now. Some manufacturers provide velocity parameters as a guide, not a hard and fast rule. Shoot water jugs if that's your interest, gelatin if you'd prefer. Heck, put some of Paul Harrell's meat targets together for organic tissue results. Dress them for a variety of events. Point is, satisfy your 'need to know' on your terms.
Now, back to the load data. Allow this information to help you achieve a velocity that will deliver the results you want in the target of your choice.
Your 6" revolver should be very accommodating. Peace.

Damn, that was so much fun. I ran my Prochrono DLX for the first time today and tested a number of loads I had. The range is outdoors but the firing area is covered so I used the indoor light accessory.

First I shot 22LR in my 617. 990fps average, sigma 76fps

Then I shot some light load 38spl with 158gr LRN, 5.2gr of AA#5 825fps sigma 6fps.

Next I shot some factory 38spl FMJ. I have no idea what they are. 970 sigma 21fps

Then I got to the good stuff that I made.

38spl with 125gr xtp and 7.4gr AA#5: 1044fps sigma 9fps
That is near the high end of the 38+p range for AA#5. They were a quite a bit slower than the speeds shown in the Western Powder v8 where 6.8gr is supposed to produce 1074fps. As pointed out, my barrel is 6" and the test barrel was 7.75"

357mag with 125 gr xtp and 9.7gr AA#5: I got 1170fps sigma 39fps
Data shows 9.6grains giving 1273fps with a 6" barrel. So not sure why mine were so much slower as boith the test barrel and mine were 6 inches.

Now that I have tons of 357mag brass, I think I will mostly just make stuff with that. So much fun to shoot. I am still grinning

Thanks or all the discussion here. It was really helpful. Its really satisfying to work on these load designs and then see what they actually do.