As a reference point regarding running a local former low-level pro said that he ran 4:30 miles in high school. At his best he was at the absolute bottom of the domestic pro scene. Around here he was pretty fast but the shorter 1-2 hour races didn't suit his training/fitness. He outrode locals mainly because he wasn't blowing up after 4 or 5 hours. In hour long races he could attack like mad and not get away. He didn't have a massive jump so it was possible to follow him, and he couldn't sustain insane speeds too long, although I certainly got ridden off his wheel more than once.
Which brings me to tactics. To be a pro you need to be pretty strong. On a relatively flat course you should be able to sustain 23-25 mph for an hour. However, once you have that strength checked off, you need also learn how to race. Learning tactics and being able to execute turns you from a strong Cat 3 into a low level pro.
Some other anecdotal bits. I think it was Roy Knickman, a massive talent back in the 80s. He did his first 10 mile time trial in sneakers and such. I think he did a 28 minute time, so about 22 mph. Within a couple weeks/races (weekly time trial) he was doing them in 22 minutes, so about 28 mph. (I've never done a 28 mph TT in my life, even with TT bike, skinsuit, disk wheel, etc.) He ended up a solid pro, better at one day races with immense strength/power. I think he averaged 30 mph for 20 km in the Junior National TT, using a 53x15 top gear (gear limit at the time).
A local Cat 1 did an FTP test at the Tuesday Night race maybe a month ago - he started the race knowing he was going to go as hard as he could for 20 minutes. One of my teammates told me they were basically going 30 mph for 20 minutes while this guy pulled. He placed 8th? at Athens Twilight Crit earlier this year, and recently got 5th in another NRC race. He's been racing a number of years but this was a breakthrough year for him.
Etc etc. Pros are just soooo strong.
That's not to say dream. Read what Lemond did when he was a Junior. He wrote down his goals and knocked them off one by one like nothing. From
here.
"I made a list of goals in 1978. 4 Goals:
Junior World Championship
Olympics
World Championships at 22
And Tour de France at 25."
I did the same list for me. Mine was a bit more grounded. State RR. Enter National RR (required qualifying by placing top 6 in states back then). Do Philly (pro-am at the time, amateurs could still enter even though it was a huge, huge race). I got to halfway into the first lap of the 10 lap state RR before my dreams ended. lol.