I think it is the same effort level / pace. If something has merit and can be put to good use, eventually multiple people will hit on it and figure out how to use it. Hence, you might see several different terms for the same thing.
I hit on this pace in high school when I was going too fast on what I thought at the time were "high steady state" runs. What I didn't figure out until later was that I was focusing on the "high" rather than the "steady state" and my pace was way too hard to use as regular "steady state" running. I found I got the best results by breaking up my runs at this pace into medium length efforts of 10-12 minutes (and would do 3 of these during a hard workout). I stumbled onto this protocol by stopping at gas stations for water and a short stretch, then would start up fairly easy again for a couple of minutes and get back into the faster pace. After college, I refined the protocol through trial and error to use a pace just above (faster than) a true tempo speed and would spend about 25-30 minutes of total work at this pace, broken into sections of 3 to 12 minutes, with 8-ish min. segments being the most effective.
When I say "I hit on this pace," I don't mean I discovered it! Others were using it as well. Even Lydiard's guys were pretty close to it on their 3-mile and 6-mile "time trials" in the late pre-season. So it's an effort level that people have often used. The rationale behind breaking up workouts into short bouts with recovery periods is the same as for any other "hard" pace; you want to amass more time at the desired speed without overcooking it than you could get if you simply ran hard continuously.
I got the term "crest load" in 1995 from Kyle Heffner, a 1980 Olympic team member and exercise physiologist. It stuck. Of course there are other names for the same pace and other protocols you can follow which use it. The common thread between these protocols (apart from the pace itself) should be paying attention to how long in each work bout you stay just above the onset of hyperventilation. Don't stay there too long, because you want to avoid a drop in blood pH. Too much distress is counterproductive when training the lactate system, as it reinforces labored movements and requires added recovery time between focused workouts.
Adding the speed maintenance afterwards helps recruit the fast twitch units after they have been partially depleted of glycogen, increasing aerobic properties in those fibers. Plus it keeps you in touch with fast stuff and has you practicing a faster finish to everything you do.
Enjoy.