I have virtually an identical system, and just completed install of Paramount nickel upgrade this past weekend. I have about 10 hours of break-in thus far, so it's a bit early to describe changes in full, but immediate impression is that the micro dynamics are much improved, leading to better imaging and fine details across the full range of frequencies. This isn't a knock-your-socks-off, holy crap-type upgrade, but very worthwhile nonetheless (in my opinion).
I love my KG5.5s and they've been in my system for 20 years, but I realize they're the weak link. The iron upgrade sets the stage for a speaker update at some point in the future and/or a switch to 2a3 configuration from 300b. Swapping out my modded Extended Foreplay III with a BeePre would have a much bigger impact I'm sure, but that's just not in the budget at the moment.
Chris