Why is my Adaptec ACS-200 Firewire/USB2.0 enclosure so damn slow?

[NeoPTLD]

Tested: transfer rate test using Sandra in USB2.0 and Firewire.
Drive used: Maxtor 80GB, 7200RPM
Interface: Adaptec DuoConnect PCI

Generic enclosure: 18MB/s USB2.0, 28MB/s Firewire. Expected result.
Adaptec: 17MB/s USB2.0, 11MB/s Firewire. Slower than heck.

The Adaptec uses Genesys chipset while the generic uses Prolific 3507.

 

[Jiggz]

I use the Prolific 3507 and has the duo version. I'm happy with its transfer rate when using firewire. As for the Adaptec, I guess brand name doesn't necessarily mean the greatest.