I have both, 2 x 120 gig agility IIIs and 2 x 120 gig M4s. Will be Replacing my agility IIIs soon with either the M4 or the Samsung 830s. Will probably just use the agility III as a storage drive, or more likely - stich them into a usb3 encluser and use like an oversized thumb drive.
Get the M4!!!!!
NOTE Benchmark. Ignore Sequencial. Also most advertized benchmarks are for data that is readily compressable, not close to real life. While using compressed data is also not real life, it is MUCH closer.