Part of the answer here’s X870(E) boards generally support DDR5-8000 at 1DPC 1R per OP query. As @quilt pointed out, the CPU may be the limiting factor.
As to whether it’s worth it, TechPowerUp’s also looked at Zen 5 memory scaling with similar results. There’s little data on associated power scaling but all of what I’m aware of is on Level1 as well.
MSI’s clearer with their specs than ASRock, Gigabyte, and Asus.
| mobo | DDR5 support |
|---|---|
| X870E Aorus Xtreme | 8800 |
| X870E Aorus Master | 8600 |
| X870E Godlike | 1DPC 1R 8400+, 1DPC 2R or 2DPC 1R 6400+, 2DPC 2R 4800+ |
| X870E Carbon | 1DPC 1R 8400+, 1DPC 2R or 2DPC 1R 6400+, 2DPC 2R 4800+ |
| X870E Taichi and Taichi Lite | 8200+ |
| X870E Nova | 8200+ |
| X870E Aorus Elite | 8200 |
| X870E Aorus Pro | 8200 |
| ProArt X870E Creator | 8000+ |
| Strix X870E-E | 8000+ |
| X870 Tomahawk | 1DPC 1R 8400+, 1DPC 2R or 2DPC 1R 6400+, 2DPC 2R 4800+ |
| Strix X870-I | 8400+ |
| Pro X870-P | 1DPC 1R 8200+, 1DPC 2R or 2DPC 1R 6400+, 2DPC 2R 4800+ |
| X870 Aorus Elite | 8200 |
| X870 Gaming | 8200 |
| X870 Eagle | 8200 |
| X870 Steel Legend | 8000+ |
| X870 Riptide | 8000+ |
| X870 Pro RS | 8000+ |
| Strix X870-F and -A | 8000+ |
| Tuf X870-Plus | 8000+ |
| Prime X870-P | 8000+ |
Edit: added Asus.
If there’s data comparing quad 1R to dual 2R I’m not aware of it, though MSI specs no difference between the two. As others have pointed out, dual 2R’s the accepted practice.
Probably not intrinsically. Quad DIMM terminates what would otherwise be open stubs from the unused DIMM sockets. Available quad data’s almost all 2DPC 2R, though and, despite lack of an evidentiary basis to do so, it’s common to conflate that with 2DPC 1R. The type of DIMM socket used likely also affects comparisons between 2DPC 1R and 1DPC 2R.
Another question I have here’s whether CUDIMM helps any with 2DPC. Haven’t seen anybody look. FWIW my guess (coming from layout experience of prior DDR gens) is there might be some benefit despite the lower clocks in 2RPC configs. Doesn’t mean CUDIMM’d be useful in making the jump from 6400 to 8000, though.