The M will be much more track 'prepped' (obviously). Pragmatically speaking the 335 will do almost everything the M will up to its (335) limit. The M has the superlatives.
GM is coming out with superb powerplants...and I underscore powerplants. Their package isn't as nice (obviously) but 505hp certainly says a good bit and IMHO nothing sounds as good as a pushrod 8 wailing.:rocks: