Fixed this problem by using Hitachi's Feature tool:
http://www.hitachigst.com/hdd/support/download.htm I burned the .iso, booted it, changed it - it's pretty easy to figure out the utility - and voila!
Now I get 12.2ms seek time with the highest numerical AAM setting. Seeks are definitely more noticable though but I don't mind HD seeks, I suppose I could mess around with it a bit and find a better noise/performance balance but I'm not going to bother right now. It also seems to 'stick' after reboots and power downs. I just hope this doesn't somehow damage the drive :p I know it shouldn't because it's not running out of spec or anything but it almost feels like overclocking the HD versus how it was before ;)