You'll get the hang of pacing efforts as you do more. It's just the way it is. We don't 'know' what our max is over a period of time until we've done it and most likely done it a few times.
"averaged 310 watts in the warm up 5 minute effort"
That doesn't sound like a warmup unless you're doing a prologue.
Find a warmup protocol and stick to it (again, you'll nail it the more you do it)
You'll get the hang of pacing efforts as you do more. It's just the way it is. We don't 'know' what our max is over a period of time until we've done it and most likely done it a few times.
"averaged 310 watts in the warm up 5 minute effort"
That doesn't sound like a warmup unless you're doing a prologue.
Find a warmup protocol and stick to it (again, you'll nail it the more you do it)
Here's some overly complicated ones..
http://www.o2endurance.com/content/?cid=42&cat1=371&cat2=286&cat3=0&level=2&id=286