You can find the speed of your SATA controller with the
System Information application, by clicking
system report > hardware > Serial ATA. Which in my case (a 15" 2.53GHz 2010 MBP) shows the following:
Intel 5 Series Chipset:
Product: 5 Series Chipset
Link Speed: 3 Gigabit
Negotiated Link Speed: 3 Gigabit
Description: AHCI Version 1.30 Supported
3 Gigabit means the maximum uncoded transfer rate is 2.4 Gbit/s or about 300MB/s (286MiB/s).
In conclusion: a 500MB/s disk is probably overkill.