All the material I've found seems to suggest just that, 3071 power with response rivaling that of a 2860.
Whether or not that's true... Well, we'll all have to wait it out. Most projects using 6258s seem to be progressing as quickly as mine, at a pace that makes glacial appear swift, so dyno charts are thin on the ground.
For the amount of money I've spent so far, I could have easily gone 3071R on a high mount manifold, and probably be back on the road a month ago.
But where's the fun in that?
*waits for the obvious remark*
While admittedly, I have hit a wall, it happens to anyone that spends long enough sitting in their personal hell garage, drinking beer, and staring at a car in bits, I'm still more than happy I spent the coin on the Borg Warner.
I looked into actual 2860RS' (instead of the high flow I had), 2871s, 2876s, 3071s, T518zs, TD05s, TD06s, RX6s, etc etc etc ad nauseum, I now know more about those than I'll ever have the need to, while the 6258 may not be the best 'bang for buck' for most punters, for my dollar, it was the only way to go.