Interesting that the base G 5-series is losing 200+ lbs while the new 7-series is losing 400+ lbs...and yet I think the starting weight is not dissimilar (by recollection).
Other than the i-brand, the new 7-series appears to be where they want to really show off next-gen weight savings and we would need to hope that the M5 is part of that wave (not just 200-ish lbs, which I think would be disappointing). Statements from Albert Biermann of M suggest that the M5 will be part of this much larger effort, but we'll see I guess. Maintaining my optimism...