I’m not telling this for sure, but the way I understand it, the “realtime proxies” mode helps you, when you don’t have the processing power (GPU, CPU) to grade full-resolution DPX sequences. But this needs the same HDD bandwidth reading the files (after reading it resizes it, so it’s faster to grade).
You’ll need to create real proxies, or create a software RAID:)
do you grade 2K material?