Just a note, the S screens will darken your viewfinder image. You'll be fine with anything above f/5.6 but past that point you will have a very dim viewfinder.

I'm using the stock screen in my 1V for the moment, (same with my 1D) but I have an EC-B screen available which tremendously helps manual focusing. I also have the grid screen you're referring to and aside from having the grid available I don't feel it does any better of a job with manual focusing over the stock screen.