The download links are here :
http://www.immiersoft.com/download.htm
The 312MHz X30 all seem to be reaching 520MHz without a hiccup. Since the PXA270 processor does support this speed, the speed is rock stable. Before you run XCPUScalar, set your power setting in control panel to "Maximum Performance".
The X30 high however runs reliably for several hours upto 728MHz. I have stress tested for over 24 hours at this setting and is very stable. Mario Kart runs at 40 fps with 1 frame skip and 30 fps at 0 frame skip with sound at 728MHz setting.