The new Cycles X is really cool. I do not have RTX cards but I do have two GTX 1080s that are the version just below the TI that are really good. And A render in a space scene with a space ship that has an emission shader between plates and a space HDR with some settings altered to go with real stars made out of planes with an emission shader on 1000 passes takes about 58 seconds with generic settings on everything else. But, I also just upgraded my CPU to an Intel 7980 XE 18 core processor that can get the same speed, but only on the old Cycles. The new Cycles X was super hard on the CPU renderers, which I use to be, but just got these two GTXs, which was nice. But, it would nice to have the option to render on the old Cycles along with the option to have Cycles X as well, until there ever is a fix for the increase in render time on CPUS that there is in Cycles X.
Might just be me, but I think asking the small team working on Cycles X to maintain Cycles simultaneously in their Cycles X branch is asking a bit much. The purpose of a branch is to allow devs to focus their efforts on the task at hand without having to deal with this sort of thing- if you want to use Cycles, don’t use the Cycles X branch.
I would like to help clarifying some things:
1.- Cycles-X REPLACES current Cycles, it’s not possible to maintain both, once Cycles-X reaches master it will replace Cycles, however you could always go to a previous Blender version to use Cycles as it is now, remember that Blender is retro-compatible.
2.- Cycles-X it’s an early ALPHA, any comparison regarding GPU or CPU performance, more than being a curiosity is useless since there is a ton of work that it’s still to be done, clean-up, optimization, new techniques, testing, internal benchmarking, a lot of features, right now you can’t even use more than one device, so no CPU+GPU or GPU+GPU.
It’s an early Alpha, that means that you have access to it because Blender is an open source project that wants to be as transparent as possible, and because the devs wanted the users to be aware of what it’s coming, but right now not even bugs are accepted for Cycles-X, and the branch can totally fail at any given commit, so it can fail today and it’s not a problem.
No one should use Cycles-X in production or with production expectatives because it’s not at that point, it’s not even an advanced Alpha, it’s an early alpha.
3.- Cycles-X will be committed to master when it’s ready, and that means that devs will decide WHEN it can be considered ready, it needs to meet several requirements, like performance, feature set, stability and much more, so it won’t replace Cycles at will, but with a bit of luck it may reach 3.0, however it has been always planned for 3.1, so I would not hold my breath for 3.0, if it has to wait until 3.1, so be it.
4.- Cycles-X is a major rewrite, so internally many things are changing, once again, let me stress this out, don’t compare Cycles-X with anything, it’s not ready.
If you have a custom build and lets say you compare it with Cycles-X, be sure to not say something like “my build is X times faster than Cycles X with two GPU’s”, mainly because Cycles-X don’t support more than one device, so refrain from doing comparisons, it’s not production ready AT ALL, it cannot be compared.
Now if you want to benchmark it as an informative testing, awesome, go for it, but always remember, it’s an early alpha, nothing that can be compared with a production ready software.