I changed to M1 0W-40 at 5000 miles on my SI. So far the engine hasn't grenaded or anything. I haven't noticed any change in power and i'm getting the same gas mileage as before the change. So far so good. I'll try and get a sample for analysis when I change it out.
I have an oil chart for the Japanese Civic Type R (same engine as the RSX-S)that I found on the Honda Japan web page. It calls for 5W-30 or 5W-40 across the range from -30 to 40 degrees C. And 10W-30 from -20 C up.
