Typically the even numbered models use the same chips as the previous odd numbered models so it probably wouldn't be more efficient, just more hashrate. If they introduce another higher hashrate with the same chips it will probably be an S7+ though. The next jump in efficiency should be an S9.
Also just putting it out there but last night I lost internet for 10-15 minutes, didn't find out until this morning, and both of my S7's set to 60% manual fans did just fine. One is batch 5 with original firmware and one is batch 8 also with original firmware.
There may be a possibility of a higher chip count system running a lower average clock rate as an incremental efficiency increase...
Is that what was done with the S4+ and the S5+?