"all things being equal": I've got no antivirus on my Linux machine, but kmail2 consumes lots of CPU-time. All kind of background processes might cost speed. So it seems quite difficult to compare let's say a texlive installation on Win7 to it on openSuse 11.4.
The editor should not affect speed, except for maybe fractions of a second.
That said: I'd be surprised if texlive had the same speed on both OS's, regardless of lenght of the document and the number of used packages. But to compare it, you'd have to test many documents and you'd have to take provisions to keep each OS from doing something like indexing the harddisk during compilations.