Improvement from using RAID

I got a RAID card a few weeks ago and I have be using it without any problems.
I have two Seagate U10 10GB 5400rpm ATA 66 drive.

Previously, when I benchmarked my HDDs read speed, I managed to get 18MB/s. Both the HDDs are connected to the primary IDE channel.

Recently, I bechmarked my HDDs again and managed to get 27MB/s (read speed). I am using striped mode for my HDDs.

Can I trust the benchmark results ? Another thing I wonder is, why the drives can’t reach even ATA 33 speed ? However, I didn’t notice much improvent from my HDDs in real life.

when normaly using your system you wont notice if a HD works at 20Mb/s or 40Mb/s
because you hardly ever use the full bandwidth of your HD.
bandwidth only is intersting if you’re going to run a server or something like that.
with normal dektop usage you have plenty bandwidth with ATA 100/133.

on the other hand it looks good on your performance graph
but you wont notice in everyday computing