I've had one of these for a year (2x8GB of the RGB variety) running at 3200 MHz on Ryzen 2700X with MSI B450 Pro Carbon. They have an automatic default speed of 2400 MHz and two XMP profiles with 2933 MHz and 3200 MHz.
Added another one for 32 GB recently (one year later), Machine would not boot at 3200 MHz with 32 GB, not even POST. Swapped the sticks around trying all combinations and it worked in a few others. New sticks in slots A1/B1 and old ones in A2/B2 offer the highest speeds.
4 sticks worked fine at 2400 MHz in any slot config. In one it worked at up to 2666 MHz and in two others it POSTed at 3200 but was unstable. In the worst of the slot configs none of the XMP profiles worked. In the best all configs worked but only 2993 MHz was stable.
Attempting to set custom timings I found (via Thaiphoon burner) that the two sets (of the same model, bought a year apart) were in fact manufactured two years apart and had different RAM chips. In other words they were mismatched.
Any combination of two sticks (from old and/or new sets) would work just fine at 3200 MHz but not all four.
Ryzens inter core cluster CCX speeds are dependent on RAM speeds which means at lower RAM speeds some core to core to communication will be slower. This speed is usually the physical RAM clockspeed (half of DDR frequency). Having said that desktop Ryzen's 2000s max rated RAM speeds is 2993 MHz and anything beyond that is overclocking. For 4 stick configs officially AMD only guarantees 2133 MHz.
Currently running it at 2933 MHz via an XMP profile and performance in CPU heavy benchmarks like Cinebench R15 are at around 99.8% of the 16GB 3200 MHz speed. Having said that speeds in apps like Photoshop and Audacity is much better with both apps starting up virtually instantly and running like greased lightning and Unreal Engine 4 doesn't slow down after a while especially after multiple undos. So real world performance for me at least is much better.
The moral of the story being if multiple RAM kits are being paired together (even of the same make and model) they should probably be bought at the same time from the same vendor to ensure internal components tally and they can work at their maximum rated speeds.
| RAM | 32 GB DDR4 |
|---|---|
| Memory Speed | 3000 MHz |
