I truly think these comparisons are useless as most will ignore objective data and refer to subjective "data" points to make their case.
The S55 was developped in an era of ever increasing emissions/fuel consumption regulations and post financial crisis cost cutting through platform sharing initiatives. This simply cant be denied.
Does that undermine the performance of the S55? Undeniably no, by all preliminary figures it is a powerhouse waiting to be uncorked. M seems to have clearly made the most out of the base N55 and in that perspective they deserve praise.
The S65 was developped in an era of sky high R&D budgets through BMW's F1 involvement. It was built on the amazing platform that was the S85. They reach the pinnacle of what was the M philosophy at the time; race car engines in casual clothing. Instead of being governed by regulations it was inspired by its competition such as the RS4 4.2 FSI and 6.2 AMG.
I do believe, had regulations been not so strict, BMW would have retained a small displacement V8 and would have introduced new tech (DI, FI, hybrid, etc) to add power. There is simply no replacement for displacement.
This is however wishful thinking and something we will never truly know.
The S65 is technically 10 years old and is showing its age versus the new crop of engines. I own one, and have test driven the new M3, the feel and experience are completely different and is entirely up to the customer to determine what he likes best. The new S55 is more powerful, more flexible, consumes less; it is the right engine for the job required in 2014.
At the end of the day, the new M3/4 is a better car than its outgoing model, not Surprisingly. M has changed; if you don't like their philosophy there's always Porsche
Enjoy them in good health, they're all a blast anyways!