iperf is as accurate as anything else machine to machine. The machine will most likely be limiting throughput. If you are trying to actually test your switching equipment without Desktop hardware(cpu, nic, memory, etc.) interfering with the results you will have to get speciallized tools. Those will not be free of course and all in one tools like a fluke etherscope will cost thousands of dollars.
there is a version of iperf that has a gui, called jperf. It's a java front that calls iperf. You might want to give that a try.
You can also just copy a 100mb file over the network and time how long it takes.