It's about efficiency. BP-Revo was most likely running his setup at a lower efficiency level, and 5s bumped it up. At least that's my guess, anyone else is welcome to take a stab at it.
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz