Kessil or Chihiros vivid 2

[Wookii]

am really keen to read more user reviews on the WRGB2 Pro.

What interests me would be: If I set WRGB2 Pro at 100% R, 100% G, 100% B, and 0% White, would it basically be the same PAR as WRGB2 at 100/100/100?

In other words, would anything I add to the white channel would be a bonus? i.e. I do not necessarily need to set the white channel to 100% (read a few comments about it being 'washed out'), but maybe add just enough white to improve the spectrum (i.e. fill in the "valleys" between the R/G/B peaks) without washing out the R and B colours?

It's hard to say, as they don't use exactly the same LED's. I theory 'yes', that is how it should work. Unfortunately in the video above he doesn't actually show the WRGBII Pro with just the RGB channels engaged manually and the white channel at zero. He does select the dedicated 'RGB' setting (timestamp 10:00) in the app which appears to show the white channel at zero, but the resulting colour rendition looks identical to all channel at 100% (timestamp 9:30), and has the same yellowish cast often seen with warm white LED's.

If you are looking to:

fill in the "valleys" between the R/G/B peaks

You can just add a small strip of white LED's to supplement the WRGBII. I have tried this myself in the past for the same reasons, and even dimmed to very low levels, it immediately washes out the colours - its a very strange effect, and I don't fully understand how it works. I suspect the better approach would be to supplement the RGB LED's with dedicated colour specific LED's such as amber, deep red, royal blue etc, but that's not an easy task.