I've a question for the experienced 400 IMers.
In prearing for the 200 bk (and and very recently also the 200 br) I have found that swimming sets of 4x50 with about 8-10s between the 50s is a valuable training tool. It allows me to practice at or near race pace, yet the rest is sufficiently brief that it "feels like" a full 200, as opposed to swimming shorter distances on longer intervals. I also find that the add-up time for a strong effort on (4x50 with 8-10s rest) is a pretty good indicator of what I can expect for a full 200 in a race.
I'm looking for a similar training tool for the 400 IM. For 4x100 IMO with N seconds rest between 100s, what value of N gives an add-up close to race time? Is this even a reasonable approach? It removes all of the change-stroke turns. Would it would be better to break at 50, 150 and 350? That seems cumbersome.