I downloaded the free trial of PR4 to test against PL6. On my system, ten Canon R5 raw files were processed using PL6 Deep Prime XD to disk in 129 seconds. The new XD/XDII in PR4 took 245 seconds to process the same images. I have not had time to compare the results, but thought the speed comparison would be of interest. I had previously compared a free trail of PR3 with PL6 and found no significant difference in speed.
By the way my system is an AMD 3800X with 96 GB of DDR 3200 ram and a RTX 2060 with 6GB of ram. The writes were to a fast internal SSD. This was a very good Windows computer in 2020 when I built it.
I just recently moved from M4/3 (Lumix G9) to Canon. I found DPXD processing essential for M4/3 above 400 ISO and it was always better on any file than not using it. So far I feel the same for the Canon R5 and RP. If I like the results of PR4 (which I am sure I will) I will be purchasing PR4 and stop using PL6. The PL6 interface is horrible, and I only make DNG files with optical corrections and noise reduction in the APP. PR4 is only a little more cost than the upgrade to PL7 and so far the upgrades are cheaper to remain current with PR- no brainer if it is good. PL6 Deep Prime XD gives me R5 files I can print at 360 dpi at 51200 ISO that are almost as good as those shot at 100 ISO. I can only see the barely perceptible difference with a loupe.
I also compared PL6 DPXD with Lightroom Denoise AT and Canon DPP. The XD processed files were superior at every ISO, far superior as ISO increased (my opinion, but I could clearly see the superior results in PS CC viewed at 50% in direct comparison0. Also, both were twice as slow as DPXD. Optical corrections only in PL6 produced better files up to 1600 ISO than either program.
If you are curious to really see the noise in your high ISO files, run them through PL6 with optical corrections only. After seeing these I am even more amazed at the quality I get with DPXD.