ultra dma crc errors are often caused by a bad SATA cable, so not necessarily indicative of a failing drive.
As regards performance of SATAII over SATA, you will only get the speed benefit of SATAII if your motherboard is equipped with a SATAII controller, otherwise a SATAII drive will give you only SATA performance.
Likewise with a SATAIII drive. It will only perform at the speed dictated by the specification of the motherboard's SATA controller.
I have an Asus PG41T-M LX3 motherboard, and as I read it supports SATAII, that means it probably has a SATAII controller?