90s, 150s or 240s - What's the Effect of Different Rest Intervals on Maximal Power & Muscle Endurance?

The upper body appears to benefit from longer rest times.

There are many studies using 90s, many studies using 150s and many studies using 240s rest between sets in standardized resistance training regimen. Unfortunately, the studies that compare all of the aformentioned inter-set rest periods are scarce.

The latest of these rare studies comes from the Islamic Azad University in Teheran, Iran. In said study, Ali Reza Rostameyan, Jamalodin Alvani and Bahman Tarverdi Zade tested the effects of the aforementioned inter-set rest-periods (90s, 150s, 240s) in physically active male students.
The subjects performed identical workout routines consisting of six exercises, i.e. 3x upper body movements such as the bench press, biceps and front shoulder and 3x lower body movements including ESCO (don't ask me what this is, I assume leg extensions), leg presses, back leg presses.

All exercises were performed for 4 sets of 10 repetitions (at 70% of the 1RM max, w/ 5% increases every week) three times per week over the 8 weeks study period. The subjects were required to adhere to at least 48 hours of rest between the workouts and 4-6 minutes between exercises. The only difference between the workouts was thus the inter-set recovery time which was either 90s, 150s or 240s.

Figure 1: What I assume (based on the sloppily translated full-text) to be the effect sizes in the different groups | the differences were not stat. significant (Rostameyan. 2015).

As you can see in Figure 1, the 150s appear to be the optimal rest-interval for this particular subject group and workout. However, the differences between the groups did not - at least if I read the crazy tables in the original study correctly - reach statistical significance.
References:

• Rostameyan, Ali Reza, Jamalodin Alvani, and Bahman Tarverdi Zade. "Comparison of different rest intervals between resistance training sets on motor and physical variables and body composition in active men." (2015).