Are we able to Up the Voltage as high as we want as long as the CPU stays within the Temperature range?
No, not if you want your chip to live. Higher voltages can cause electromagnetic degradation or some complicated name like that which basically degrades your chip (ex: needing more volts to remain stable at a certain frequency), until it dies.
There is a lot of controversy as to where this limit is exactly, but it's pretty obvious that the tolerances are a lot lower with the 45nm process. Draw the line where you think is safe. If I had the cooling, I'd go to around 1.6V for 65nm and 1.45V 45nm.