Rosewill eSATA performance

[yahoojames]

I have an eSATA/FW800 enclosure (SS-25KB2e) I purchased from coolgear.com. It is paired with a Rosewill RC-605 eSATA II ExpressCard in Mac OS X 10.5.4 on a MacBook Pro using their latest driver (Sil332_1.1.9) and Hitachi 2.5" SATA 7200RPM 100GB drive. Here are my XBench benchmarks:

Results 15.77
System Info
Xbench Version 1.3
System Version 10.5.4 (9E17)
Physical RAM 3072 MB
Model MacBookPro2,2
Drive Type HTS72108 0G9SA00
Disk Test 15.77

Sequential 19.51
Uncached Write 9.78 6.00 MB/sec [4K blocks]
Uncached Write 26.23 14.84 MB/sec [256K blocks]
Uncached Read 20.58 6.02 MB/sec [4K blocks]
Uncached Read 62.15 31.24 MB/sec [256K blocks]
Random 13.23
Uncached Write 3.97 0.42 MB/sec [4K blocks]
Uncached Write 43.87 14.04 MB/sec [256K blocks]
Uncached Read 63.78 0.45 MB/sec [4K blocks]
Uncached Read 82.78 15.36 MB/sec [256K blocks]

These are way below what I should be getting for eSATA performance. When connected using Firewire 800, I get better (but not stellar) throughput:

Sequential 63.99
Uncached Write 72.08 44.26 MB/sec [4K blocks]
Uncached Write 63.90 36.15 MB/sec [256K blocks]
Uncached Read 46.99 13.75 MB/sec [4K blocks]
Uncached Read 85.41 42.93 MB/sec [256K blocks]
Random 26.63
Uncached Write 9.23 0.98 MB/sec [4K blocks]
Uncached Write 63.12 20.21 MB/sec [256K blocks]
Uncached Read 67.81 0.48 MB/sec [4K blocks]
Uncached Read 88.74 16.47 MB/sec [256K blocks]

Can anyone else comment on their performance with this ExpressCard from Rosewill?