Alright, so I started doing some testing. I swapped out the 9900k and swapped in Z690-E D5 mobo, 12900k, crucial 64gb DDR5-4800 @ 5000mhz, and EVGA 3090 KINGPIN.
I have my setup currently at 5.5ghz for the best two P-cores, which would matter most for DCS. KINGPIN with max power slider, +100mhz core, +800 mhz memory.
Unfortunately, I didn't pick up any noteworthy FPS gains in 2D or VR. The CPU frametime was better, the overall experience in VR with a Reverb G2 was subjectively a bit smoother, but average FPS on Hoggit Syria at War with PD 1.0, VR resolution 100% was about 50ish on the supercarrier, about 5 average FPS more than my 9900k setup. For comparison, I was able to hit 600 points single core on CPU-Z with my 9900k, and I hit 882 so far with the 12900k, so the single core performance gains are MASSIVE from this data point.
Oh, I was seeing as much as 38-40gb of system RAM being used. (holy $hit!)
I think the major limiter here now is GPU. Even with a 3090 KPE, it seems to still be GPU limited. I'll continue to mess around with some tweaks, but the gains I got from going from Ivy Bridge to Coffee Lake were insane , and going to Alder Lake seems to have caught up to what the game engine can actually use as far as IPC improvements. Maybe with coming Vulkan API improvements, we will see better GPU resource use and multi-core enhancements that will help, but I am skeptical.
A note on DDR5 - seems to be working fine for me. I was lucky and got a 2x32gb kit at microcenter on release day for alder lake. I paid $449. MY OPINION: It isn't totally "Not. Worth. It". Having a D5 capable motherboard which should support 12th and 13th gen, and knowing how fast technology on D5 already seems to be moving forward, it isn't a bad buy. Plus, I had a 2x16gb kit that was no longer made. I would have had to mix and match models which I hate doing, or buy 64gb of DDR4 again which doesn't make much sense as the value of D4 will start to fall off hard once D5 beings to take hold. Sure, in a year, the tech will be much better, and D5 mobo owners and just upgrade at that point, and have a more future proofed system that allows expansion for 13th gen too under D5. Just my honest opinion.
Also, Decent DDR4 64gb kits that are 3600-4000mhz right now are still around $325-375 or even more. D5 isn't double the price, I actually paid about 28% more for the same amount of mem capacity. I was able to overclock by changing two settings first try to 5000 mhz. Sure, my latency is higher, but I haven't noticed any actual difference in gaming.