So, the price drop on Amazon in that the Crucial m4 SATA III is much cheaper than the Intel SATA II. My MBP is only capable of SATA II. Would I be able to use a SATA III drive instead?
I don't know, but since S-ATA is backwards compatible, and I employ the same reason as you, having an SSD for a future Mac with S-ATA 6.0 Gbps (S-ATA III) interface, why not do it.
I get the same read and write speeds with this S-ATA 6.0 Gbps (S-ATA III) SSD as I got with the previous S-ATA 3.0 Gbps (S-ATA II) SSD (Vertex 2, now in my iMac with S-ATA 3.0 Gbps (S-ATA II) interface), though I think it is a bit faster, but that may be just an illusion or wishful thinking. It still suffices my needs.