As far as for vcore, at stock (1.34ish) and x3 you might get 3.4 as you have found. As an x4 I would set it to 1.35 to 1.36.
Some ballpark volts that others have found as well..
3.5Ghz - 1.4v
3.6Ghz - 1.45v
3.7Ghz - 1.5v
I'm able to operate and game unlocked at 3.6 with 1.392v, but takes 1.48v to get past prime at 3.7.
If you find it isn't stable unlocked, go back to the bios after unlocking and see if you have a "three core operation" option that will let you select cores 0,1,3 or 0,1,2. That would allow you to shut down a dysfunctional core and keep the l3 unlocked. Could also be a dysfunctional l3 that might cause problems when unlocked.
Max temp for the 435 according to amd is 73c: http://products.amd.com/en-us/DesktopCPUDetail.aspx?id=611&f1=&f2=&f3=&f4=&f5=&f6=&f7=&f8=&f9=&f10=&f11=&f12=
Edit: You need to lower your memory divider before you start raising your FSB