Will putting a dual 1 ghz in to a singe 1.25 ghz MDD system be faster?

under mac os X, that dual 1ghz machine should hammer that single core 1.25ghz...

it also depends on usage, if you usually only run 1 app at a time, then you shouldn't notice much of a difference, it might even be a little slower. but if you run multiple apps at a time then the dual should be noticeably faster.

I would think that a multithreaded program would be much faster if you're running only 1 app, as well.

they will be, only if they are multithreaded. if they are not then they are bound by the speed of the single cpu unless you run more then 1 single-threaded Apps at once.

here is a example

1 program that is S.T. on the dual 1ghz cpu will run a tad bit slower then on a single 1.25ghz cpu

now if the App is M.T. then running it on a dual 1ghz will show a huge difference when compared to a single 1.25ghz no matter if its only 1 app or more then 1 app

i would not know if you would run multiple S.T Apps at once if it would show the difference between the dual or single

Would probably get much use out of one processor, while the other processor could be devoted to a single application. The kernel is multithreaded, after all, so you'd probably get a performance boost out of just about anything you'd do. (unless, of course, you can figure out a way to run the OS with only one mach task)