Yeah I hit 39.7 mph at the rally yesterday. 40 mph with just a bike helmet, a couple sweatshirts, tighty whiteys, jeans and gloves on a mountain bike is smooth enough, but the pavement just seems so unfriendly on it's terms.....
I hear your clutch a bit. Speed shifting.....we all do it (but it's not recommended).....so far the only thing is my derailleur went a bit out of adjustment so at 38 in 5th it tried to slam into the next gear, nothing a little adjustment won't fix, but my wife was wondering about the poop stains in my.....well tighty whiteys.