200/s
A DIN port carries roughly 1000 bytes/s, so about 320 three-byte CC messages per second — shared with everything else on the cable. Keep the cap well under that if you are also sending notes.
Per-lane rate is the ceiling for that lane. Values are only sent when they actually change, so a slow-moving lane costs almost nothing.
Both the cap and the lane rate count messages, not updates. A 14-bit lane spends 2 per update and NRPN spends 4, so raising resolution lowers the update rate rather than quietly multiplying the traffic.