If you're not using a macro/script, don't bother with the 5K Pro Run. You'll hurt your hand.
Stick with the 2K Amateur Run. It's less than half the distance for half the max reward. You'll actually progress faster this way. Since the 2K length ends earlier, you can then upgrade and start another 2K race at a higher reward rate. That's 30 minutes at pre-upgrade and 30 minutes at post-upgrade rates. Winning a 5K race means you get 60 minutes at the pre-upgrade rate after spending more time racing than two 2K runs.
The 2K Amateur reward is also identical to the 2K Pro Run. The Amateur races have slower competitors, so you can use a more relaxed pace without worrying about dropping to 2nd place. Just put your fingers on the ← and → keys and bounce your hand or forearm. No need to alternate fingers.