one of the main variables that say determines how fast you can go over a long period of time is how efficient you are at propelling yourself.
My VO2 max and my Lactate threshold havent improved much over a 3-4 day period. Here is an example of how much a difference slowing things down and rolling smoothly through turns and over things effects speed.
Here are 2 rides I did - same bike / same trail - the only difference is that I actually road more off road on the second attempt. In just 2 rides between the 2 I was able to follow Gregg and follow Rob Roberts and Scott. By following their lines and learning how riders that are better than me roll through corners, I was able to make a HUGE gain in speed and at the same time work WAY less. I noticed there was something all 3 of these guys did - SLOW DOWN - they didnt make sudden herky jerky movements - they just slowly let the bike track and kept their momentum up by doing less. By going slower into the corners, your exit speed seems faster and you dont have to waste watts/power pushing hard to get back up to speed.
ride 1 - distance 43.49 miles / time 3 hours 42 minutes / ave speed 11.8 MPH / ave HR 151 BPMhttp://connect.garmin.com/activity/64338260
ride 2 - distance 46.67miles / time 3 hours 47 minutes / ave speed 12.6 MPH / ave HR 151 BPMhttp://connect.garmin.com/activity/65020179