Ollama doesn't currently support mixing CUDA & ROCm. https://github.com/ollama/ollama/issues/3723#issuecomment-2071134571
One thing to keep in mind about adding RAM your speed could drop depending on how many slots you populate. For me, I have a 5700G and with 2x16Gb, it runs at 3200Mhz, but with 4x16Gb(same exact product), it only runs at 1800Mhz. In my case, RAM speed has a huge effect on tokens/sec, if I have a model that has to use some RAM.
You can check AMD's spec page for your processor, but they don't really document a lot of this stuff.