Keep in mind that wind etc play a part at pro speeds. They'll slow for switchbacks, speed up for the straights, and if they're sheltered from the wind they can get going pretty well.

There's a story about a (new to covering cycling) journalist that was on a moto in a race on some climb (this was in VeloNews or Bicycling or something like that). The much-more-experienced driver was trying to be "user friendly" and was commenting on various things, speed, grade, etc. The driver said, "They're going 25 so that's a decent pace". The journalist, a US person, did the conversion. 25 kph is 6+6+3mph so about 15 mph. Okay, that seemed reasonable, but a bit slow. The journalist asked, "wait, they're going 15 mph?" "No, no, no," the driver replied, "They're going 25 mph. I converted from kph for you."

Pros are soooooo fast.

I went to watch the Philly race a bunch of times. One year Sean Yates won, solo. I was on the finish loops and didn't see him at all. I only saw the motorcade blasting by but not him. I didn't realize until after the race that the motorcade was just behind Yates - they were going so fast, in the 35 mph range, that I didn't think a rider could stay with them even temporarily, forget about 150 miles into the race (the neutral start is usually in the 30-32 mph range, so fast that when a domestic pro flatted he couldn't get back on, the team sent two guys back, and it took them forever to get back on the field). When Yates won I'd been racing 13 years, I had watched the (then amateur-only) National Crit Championships, I'd raced in Belgium (for only 3 weeks) where in my first race I got shelled in 5 km when my max speed was 43 mph / 70 kph (on a flat course with cobbles)... I thought I understood what "fast" was but I didn't. The speeds pros hit and maintain are incomprehensible.

At a local race (that I promote) one domestic pro team sent one of their stronger riders, sort of for entertainment value. It's sort of like if, say, Cancellara showed up at a local club's TT (but this guy was no Cancellara). On the first lap he went to the front and started pulling. Only 5 guys could hang on his wheel after one lap. 1 guy was left after two laps, and that guy got 3rd at the Elite (aka pro/am) National RR Championships a few years prior, so that guy was an absolute top level Cat 1. On the third lap the Cat 1 was gone. In about 8? 10? laps the pro lapped the field. He hung out at the back of the field and chatted for the rest of the race. He made the local Cat 1s and 2s look like Cat 5s doing the first race of their lives. Really incredible.

So he's strong, right? Well this domestic pro team went to Tour of Georgia. I expected to read at least about that guy, like maybe he'd place top 5 or something, some unexpected domestic team's surprise rider. Nope. The only way he could get any publicity was to attack at the start of a long flatter stage. He was away for something like 80 or 90 miles but faded hard long before the finish. The team was absolutely destroyed in the race. I ended up looking for their riders from the bottom of the results page, not the top.

A friend of mine raced in Europe for 7 or so years, pro. Never made it to the big teams but raced for the feeder teams. He'd come back for vacations, visit his family, etc. He came to my race. He attacked early on, got away solo. Because he's a local, because everyone knew him, because everyone knew he was a pro, everyone chased, and I mean everyone. The field was single file the whole race, going flat out. He never got a big gap, max 20 seconds or so, most of the time literally just 10-15 seconds. Yet he persisted staying out on his own. Me, personally, I'd have sat up if I was soloing for, say 20 miles without getting more than couple hundred yard lead. He got caught with about 600 meters to go, where I happened to be marshaling. I went back to the finish to do race promoter stuff and saw my friend. "I'm sorry you didn't win, I can't believe they caught you with half a lap to go" "What do you mean?! I won the race!" "You won?!" "Yeah, when they caught me I just stayed on the gas, led out, and dropped them in the sprint!"

A later year a Kenda/5-hour pro did the same series of races. He could win solo (lapped the field, but not quite so decisively as that one guy). He won a few races - it was so hard to beat him. I asked him one day if he gets tired of winning. He laughed. He said that in a pro race he's everyone else's b*tch. He says after he wins a race or two here he won't win for the rest of the year. (Disclaimer - it ends up that he had some kind of cancer at the time, didn't tell anyone including his team, but he's recovered and has won a couple races here and there, but not many people would know who he is.)

Someone posted something maybe 5-7 years back comparing wattages among amateurs and pros. They realized that the magnitude of difference between a Cat 5 and Cat 1 is LESS than the difference between a Cat 1 and a higher level pro. In other words if you become a Cat 1 you're closer to a Cat 5 than to a Euro type pro.