Need thoughts on my RAID5 performance

Hello guys.

I bought myself a RocketRaid 2320 [URL coming up] late June, thinking I'd get performace for my buck.
This week though, I've been wondering if the buy wasn't all that great after all - take a look:



My specs:
Asus P5W DH Deluxe Mobo
Core 2 Duo E6700 (2.66GHz) CPU
2GB PC6700(800MHz) DDR2 RAM
74GB Raptor System HDD
RocketRaid 2320 RAID controller
The raid consists of 5x500GB Samsung Spinpoint HDDs in a RAID5 config.


After bumping into several aricles (yeah, the raid-discussion is heated up like never before..), I've eventually found my controller to be a software controller, which, according to my readings, isn't that good. I mean, take a look at this graph, at the part 2 of Tom's "RAID Scaling Charts, part 2" It doesn't really correspond to my setup; Tom's avg. reading rate on a RAID5 with 5 HDDs is at 301,3 MB/s, while my setup doesn't even touch 90MB/s, with 87,4MB/s.
My system can by no means be considered the bottleneck here. I'm therefore speculating that the bottleneck could be the controller design; being a software controller - is this true?
I thought $440 should've been reasonably expensive for a quality controller - guess I was wrong .
I'm considering doubling the 'investment' to $895 to get 'reasonable' quality with the "Tekram ARC-1220" - that's the price here in Norway, anyway..


Any thoughts are greatly appriciated!