Yes, a 2.53 would outperform a 2.6! Why? Because it has the "533" bus. It runs at 19x133, while the 1.6 runs at 26x100. So the bus has 1/3 more bandwidth on the 2.53.
The thing about the multiplier has to do with overclocking. People will buy a "400 bus" processor hoping to overclock to the "533 bus" and get free speed. That works with the 1.8 Northwood, making it perform like a stock 2.4/533. But 26x133 is 3466MHz, nearly impossible for any current P4. So not only do you get the low bus speed with the 2.6, but you also loose the ability to get that bus speed back by overclocking.
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>