I recently posed a similar question in the addicts thread before I did my first century. I got a ton of good advice, but because I don’t have all the gadgets yet, whyfi advice worked the best. Instead of trying to control my speed, I just focused on my heart beat. I tried to keep it low throughout the ride and it worked. It also didn’t have that big affect on my speed. Remember why you are on the bike, it’s to have fun.