I am interested in upgrading my wheels to a good mid-level but would like input. My current bike came with Mavic Aksiums and I would like to upgrade to something lighter and/or more aero. The region I ride in is mostly flat. Typically I ride 3-4 group rides a week of 30-50 miles @ 18+ mph. I have been entertaining the thought of either upgrading to Krysium SL's, or on the other end, something like the Sram S40 or S60. I have been following the bike build threads and these wheels have all been suggested. It would be helpful to know what people think of either of these choices or can refer any good reviews for wheels.