ideal - ideal (as kernel-config creators think).
lv - Low voltage (lower voltage than normal)
ulv - ultra low voltage (lower voltage than low voltage)
xlv - extreme low voltage (lower voltage then ultra low voltage)
starving - lowest of predefined settings (lower voltage than extreme low voltage)

So starting from lowest voltage it's: starving < xlv < ulv < lv < ideal.

You can try xlv and if it crashes, try ulv, if it still crashes then lv and if it still crashes -> ideal. You need to check if it is safe, worst thing that could happen is your device rebooting and restoring default values. I use ideal profile since I can remember and I'm quite happy with it.