I'm now on week 7 of C25K and have been doing all my running at the local gym on the treadmill on a 5k program that gives me a little course outline, and randomly varies the incline between 0.5 and 3 degrees.
More often than not, I've been finishing out the 5k track on the screen with a mixture of walking and jogging after the cool-down walk has finished. In this way, I've already completed 5k many times as a mixture of running and walking.
My first 25 min run I completed 16 mins @ 6/mph, 4 mins at 5.5/mph, 4 mins at 5/mph, 30 seconds at 5.5/mph and 30 seconds at 6/mph. With the two 5 min walks @ 4/mph, the session covered about 4.5 km, and I finished out the 5k with a time of just under 36 mins (down from about 42 when I started out).
I'm doing a 5k Zombie Evacuation Race on 28th of September, but my local park run does pacer runs on the first weekend of the month. There are a pair of pacers doing 35 and 34 min runs, and that means that if I want to get a good idea what my treadmill pace feels like in the real world, I could to do the parkrun next weekend, it would probably work out as the week 8 run 1 or 2.
As I see it I've got five choices.
1. Do the park run (7/9) with the pacers at week 8 run 1 or 2
2. Do the park run (14/9) without the pacers at week 9 run 1 or 2
3. Do the park run (21/9) without the pacers as a graduate
4. Do the park runs starting tomorrow (no pacers) and walk where I have to, after all I "can" technically complete 5k already, then do the pacers next week.
5. Hold off on park runs until after my zombie evacuation race on the 28th.