For anyone who's wondering, a bit of homework with the major parts suppliers here in the UK suggests a 50-60% price increase is typical moving from (new) Red to the Red Pro of the same size.
Higher RPM drives also generally have a slightly lower linear density (the TPI should generally remain the same), meaning for the same capacity they require more platters. Frequently with little in the way of throughput increases (due to said lower density).
The one thing faster spinning drives do buy, is lower seek time because rotational latency tends to be the largest contributor to average seek.
That is part of the reason you don't see a lot of drives spinning faster than 7200RPM these days. SSD's ate the market which wanted speed over capacity,
I've been patiently waiting for 3600/4200 RPM 5.25" drives to make a comeback.. <chuckle>
