The max CPU VTT for the Core i3 500 and Core i5 600 series is 1.4V.
Do you have a link to this information? I know that the Lynnfield CPUs spec
state a max of 1.155V and an absolute max (thank you Intel) of 1.210V but I haven't seen the Clarkdale specs. I wouldn't mind giving the Clarkdale specs a read.