If the file page you're jumping to is already in the kernel's disk cache, this is a win. But if getting to the target page requires moving the disk head, you might be better off with a sequential scan. For an infrequently accessed file in the 7-8 disk page range, I suspect that the linear scan might win.

I think we're in the toss-up category.

BTW, this is a tricky one to test by profiling, since you may have to go out of your way to make sure that the file isn't cached.