SCA adapter

Hmm... I'm having bit of a dilemna. I recently got myself a SCSI setup, but I've run into problems getting it to run at the proper speed. Eventually, I came to the conclusion that it is the SCA adapter I have that's making it default to the speed of 40 MB/s instead of the 160 MB/s the bus should be running at. I've checked literally everything and the only thing that's suspect is the SCA adapter.

Could anyone recommend me an SCA adapter that they know works for sure?

Here are my specs in case you have any other ideas:

Seagate Cheetah X15 ST336752LC
Adaptec 29160N
Amphenol U320 cable w/terminator attached

I've used many different kinds and never had any issues, but have heard of others with problems. I've used some from here, but beware of shipping costs:

http://www.cableclub.com/product_info.php?products_id=1307