tankerkiller125 I get what you mean there, I've had the same experience.
I can make the app run at peak load at least, and then we're scoping for like 50 devices on a site, so the bandwidth of the app on one machine multiplied by 50 should get me there, it's just working out how to monitor.
The best I've got is maybe putting a PC on a bench and setting up a network just for it, then running PRTG (or similar) on that network and then taking the peak as the per-device load? Sounds like a PITA... though I can't think of anything better atm