Raced at southern xc today in the open on SS for the first time, still have to wait till find out result but somewhere in the top ten i think and it may be my best result yet! Only raced with gears before but i seem faster on my SS (think i am just rubbish at using gears properly).
I would agree with the other post that if you wish to go as fast as you can and know / learn how to use gears then you will be quicker than on SS.
However i race for fun and just prefer riding SS so that is what i am sticking with. I also ride with flats for the same reason.
As to gear ratio i was using 34 front and 18 back on 26 inch wheels, But think i would have been better with 19 on back for the course at Pippingford Park. I suggest you have a couple of options with you at a race then swoop if needed after practice lap. I have found that for my level of fitness the standard 2:1 is to high for decent XC race courses. To compare, If i am riding in the new forest then i would use 36 at front and 16 / 15 at back.
Hope this helps