Why did you short stroke the drive? You only lose capacity.
As for your read speeds, what are other people getting? Remember everyone can have different setups, chipsets, etc.. that can affect performance.
I have 2 x Western Digital 500Gb Caviar Green HDDs in Raid 0 on a Asrock 880G Extreme 3 MB I get Min 75.8 Max 190.5 Avg 138.9 Access time 18.5 Burst rate 160.6 CPU usage 5%, this is worse than yours is there anything I can do?
Using HDTune to test a RAID array will not yield correct results. You need to use something that tests on the filesystem; not artificial raw read. ATTO, CrystalDiskMark, AS SSD, Sisoftware Sandra and HDTune Pro's File benchmark do this; but the regular HDTune or HDTach is not recommended for RAIDs as you can get incorrect results.