A subject close to my heart right now: I'm relatively new to the darkroom and just last weekend I finally got my first bottle of Kodak Selenium Toner. I also picked up a copy of PhotoTechniques with an article about using it. The suggestion there was to tone MGIV FB for 8 minutes at 1+10 in working strength HCA for maximum Dmax, so it seemed like a good place to start. Having read about how MGIV doesn't really tone I was expecting to be on the lookout for increased Dmax. After studying for a while I can probably convince myself that there is some Dmax increase but the real change is the colour; it's definitely turned bluer or perhaps the word is charchol. I love it.
As I had some, and I'd heard about how it tones so much more, I also tried some Warmtone FB. I'm not sure I really like Warmtone untoned, a bit too warm for me, but I like the change the selenium produces very much, although I can't see that it's any more of a change than that I can see in the MGIV.
But then the next day I took my comparison pictures into the office where half dozen souls were cadjoled into passing their judgement. Not one of them, without prompting, noticed a difference between the toned and untoned. On either paper!
Oh, everything developed in Ilford Multigrade Dev. And, as I can't get anything other than Ilford paper, and have less than a year's experience in the darkroom, I can't comment on how MGIV compares to other papers. But, as I said, I do like what I see, so do have a go and see for yourself.