How about, is it harder to run a 14:30 5k or become a Cat1 cyclist?
My answer: 14:30 5k
Here's the reasoning for my bias:
If you run a 14:30 5k, you have the athletic ability to become a competitive CAT1 cyclist. Ofcourse you need to develop the specific muscles and most importantly, the skillet to actually race a bike. I feel that n running, its 100% talent + conditioning and drive; in cycling its 85% talent + conditioning/drive and 10% Racing smarts and 5% luck (being on the right wheel at the right time whether in breaking away, avoiding a crash, or sprinting home).
I was a D2 14:30 5k guy who took the plunge into road cycling a few years back because of injury. I've been in the 3's for a while, but I'm not serious about upgrading. A lot of guys I beat on the bike the past couple of years are now 1's or 2's, but they race more in a season than I did in 3 years! Also, if you're a master (+35), you have two to three times as many chances to place and get upgrade points. In running,
On the bike, I've found that 7-9hours per week gave me a variety of strengths needed to race and place well in a variety of races at the Cat3 level. When I had the time to ride more like 12-14hours per week, I beat a lot of solid cat1/2 guys in 123crits(I'm not a sprinter), time trials and group rides (which really become races). Most of the young guys I know (<23years old) who are serious about racing and possibly getting on a domestic pro team are riding 15-20hours per week. I did not train (running) more than 10hours per week in college to run my pr's. I think to reach a similar level of competitiveness on the bike I would have to train 15hour+. The demands of 90min crit or a 90mile road race are alot different than 5k/10k.
I found that the Time Trial was the most similar in terms of demand (physically and mentally) to running.
I was about 74kg when I ran my pr's of low 3:50's (1500m), 8:20's (3000m), and 14:20's (5000m). I feel that I can ride/race against most Cat1/2 guys in California while producing about 4.72watts/kg at threshold. Learning patience and race strategy has been a lot more challenging than anything I was exposed during running. However, if you blow up in a running race, your not coming back; in a road race, I might find my legs again, catch the break away, and get a top 5 finish....
I think cycling allows a wider variety of athletes to be very competitive. Cycling Categories shows a rider's racing success, not necessarily physical talent. In running, we go by pr's.
By the way, I'd be glad to start a CA based cycling team of former runners and see how we stack up against other teams. We could about running while cycling.....