Heat is heat.
You will have less heat on the Northbridge. CPU Freq is CPU Freq.
It's something like:
Wattage = Voltage^2 * Frequency * Capacitance
So... In theory FSB/Mult has no effect if the same frequency is attained. But the area around the CPU will be warmer from a higher FSB because of heat generated from the Northbridge.
That said.. Higher FSB = More Performance.