The MIB is showing the total number of requests since the box started. To get RPS you need to probe the MIB, wate then probe the MIB again Using those numbers subtract the first sample from the new sample and devide that by the time interval between the 2 samples.
e.g at 13:00 sample mib and get 1000
at 13:05 sample mib and get 7000
7000 - 1000 / 300 = 20RPS
I have a ruby script that does this and out puts a small html page with real time numbers. and I also I use cacti to graph the numbers over time.
I'm happy to share the ruby script if it is of intrest, and the cacti config is very similer to how you would setup a network interface.