Your CPU manufacturer should have a data sheet or specification page on what the max safe operating temp is.
AMD Overdrive is as reliable as the hardware sensors which tend to freak out sometimes in my past experience.
If you want to overclock, you're going to have get over the idea of not adjusting voltages. I'd say that guy who said they got their clock frequency by adjusting multiplier and bus speed only was full of crap. I'd like to talk to him. And see a CPU-Z validation of before and after and an array of stress tests to prove its stable.
Every motherboard is different. Overclocking requires a lot more power. 600mhz overclock on one review I looked added more than two or three watts of power consumption that's for sure.
Anyway, you need high quality parts and cooling to overclock successfully beyond a few hundred megahertz. So, Just adjust some voltages and see if you can get the o/s to boot. I'd say if it was me and I wanted to do a speed overclock. I'd start by raising CPU, CPU-NB and NB by .01 to .02v for every 100mhz. Then give it the smallest increments on one of those at a time until you boot successfully.
It's really all up to you. That's just how I did mine. There's no rules when overclocking buddy. Anyone who tells you you're wrong is the one who's wrong.
You can ease off the voltages one by one until you find out which one was the major factor in that frequency attempt. BE SMART! That's all I can give you until your next reply.
EDIT: This is assuming you don't change any bus speeds of course. You may do that if you want but, you may have to increase voltages on more than just those 4 major components.