Hi Bruce. Since no one else has chimed in, I'll go ahead and share my usual procedure. Kentmere Fineprint glossy (VC, fiber) is my normal fiber paper, and I usually tone in KRST 1:20 for 3-4 minutes. When I first began doing this I carried out some tests which did show enhanced dmax but minimal color shift at those times. I haven't dug my notes out, but I do remember that there is a subtle shift to purple blacks if you go much beyond that. If I can find my test prints and notes I'll update this post. I do recall that all the changes I saw (both in dmax and color) were subtle and might not even be noticed without side-by-side comparison prints. Hope this helps!

--Ben