The standard caveat regarding runner ability:
A lot of what I’m about to say below assumes you’re not a hardcore runner logging elite-like volume (70+ miles per week).
When you’re pumping out 70+ miles a week, you probably already run high-volume speed workouts like this on a regular basis, and can probably run the Yasso’s at a strong pace, such as your 5K pace or better.
For experienced runners relatively new to the marathon:
The more volume you run per week, and/or the fewer marathons you’ve done, the more you should scale back the Yasso projection.
e.g. if you run 100 miles a week and can run 800’s in 3:05, maybe estimate something closer to 3:20 for your marathon. Or if your 20 mile long run is the first time you’ve ever run 20+ miles, scale those 4:15 Yassos back to a 4:30 projection.
You should already be running a lot of miles.
If you’re training for marathon, you should be logging more than 20-30 miles a week during training. Probably way more.
40-50 miles is probably the minimum during marathon training that will produce a good marathon effort, assuming you don’t already do several marathons a year.
Personally, I feel a lot of self doubt having run 30-50 miles per week, even though many would say I’m in pretty good shape to run my next marathon (while many experienced runners would say I’m not even close).
Speedwork is not a race. Don’t run the reps like a race.
As with any interval workout, you should not race these reps: Don’t do them hard. Don’t pick up the pace and “kick” at the end of the rep.
Run every rep with a steady effort wire to wire, where once you finish you could run another few miles at that exact pace if you had to.
The reps in the Yasso workout are supposed to be a barometer of your capabilities. Running closer to your max effort will not give an accurate picture of those capabilities.
These Yasso paces should be easier than running a 5K
According to most reliable pace charts (Daniels, McMillan, etc)… you should be able to hit a desired Yasso goal at about your 10K pace or slower.
If you give more like an 8K or 5K effort to hit your pace on these reps, not only may the workout be inaccurate, but (unless you run 100+ miles a week and do workouts like this all the time) you probably won’t maintain the stamina to nail that Yasso 800 pace consistently for all 10 reps.