I run Shell Rotalla T6 Synthetic, 5W-40. The "5W" is its Winter weight/viscosity. It is only 5 when it is cold; it thickens up to 40 as the oil warms up. No issues in any of three bikes, and three 4-wheeled vehicles running it. Putting it into my small engines as well. Honda recommends 10W-40 oil for their 750's, so a 5W-40 is just fine. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII