Played around fairly extensively with the trial version of PL6 and came away quite impressed with the DeepPrime XD noise reduction, which is significantly more effective in removing noise than the regular DeepPrime and also better at retaining meaningful detail. Encouraged by SmugMug's recent announcement that they now retain wider colour spaces of uploaded images, I also gave the DxO Wide Gamut a try, which indeed leads to richer, more natural-looking colours on my BenQ SW2700 when I switch it to AdobeRGB. I did notice that with some images I will have to use the "Protect saturated colours" slider a bit more to avoid colour clipping, but the results still look better than before.
I will upgrade from PL5 as soon as my budget allows, although I'm hoping to get a slightly better deal when my trial expires or in the Black Friday sales.
Here are some samples, utilizing both DeepPrime XD at "magic wand" default levels and the Wide Gamut (K-3 at ISOs 5000, 4000, 2000, and 500, respectively, all processed to taste; you can view full-res JPEGs on my SmugMug website by clicking on the samples):