This is a very difficult question for us to answer because it does not really depend on the number of Users but rather on the number of connection requests per second that we get. So if you have an estimate of the average number of simultaneous or concurrent users and how many requests per second each one will generate then we can answer easily. Our competitors argue an average of 3 per concurrent user which itself is an average of 1 in 10 total users. Our experience is different almost every time.
Anyway we can handle 60 requests per second on an unmodified OP1400 and 150 if you buy our cache accelerator which is essentially a second disk drive and channel (specially configured of course). If we use the figures mentioned above that gives us 200 and 500 users. We do not recommend using these figures. If you have over 120 users we recommend the accelerator and over 300 we recommend that you get a separate Cache server or array that is designed for higher volumes and we have a whole range. We still use your original OP1400 to do the redirection and Bandwidth Management of course.