Low random access/write perf

[eX&TriC]

I've got aTh7II (i850 chipset) with a UDMA/100 controler
2 maxtors are connected to IDE1. IAA v2.3.0.2160 installed
drives are UDMA5 In the bios everything is on auto/performance

My problem is the low random read/write that cause games
to run choppy when fetching data (I got ti4600 & P4 2.4 and mafia is unplayable at 640x480)

I already tried this:
- different cables
- drives as master only
- different combinations with drives
- different IAA

Are there maybe any biossettings that could cause my problem??