Supported transfer modes:
K7T Pro: ATA33 & ATA66
K7T Pro 2: ATA33 & ATA66
K7T Pro 2A: ATA33 & ATA66 & ATA100
According to Anand, the ATA100 capable 'B' version of the southbridge used, among others, on the Pro 2A is up to par performance wise with the Intel solutions, whilst the ATA66 'A' version performed much slower than the competition. So wether or not ATA100 is something you need or not, the Pro 2A will give you better performance simply cause it has a better of the UDMA protocol.