Unless you have lots of heavy scripting, or flash components, then you probably won't need to worry about it. If you're worried, then you can check via the chrome developer panel the actual CPU time spent rendering the page. This can be translated directly for slower processors. If you really want to tweak it, then you'll need to get a program that will "spin" the CPU at a set rate, and adjust it's priority level (can be done via Windows API).
You could design a program yourself, and have it poll the maximum clock speed of the CPU, then run "pointless" calculations for a percentage of each timeslot. When you're doing this, don't go for anything too complicated, since this can actually overheat and damage the processor.
Also, Flash uses hardware acceleration. Badly, but it uses it. That means that you may not see any impact on the performance by changing the CPU, but changing the GPU (nowhere near as easy) will impact performance by a ton.