The Alpina B6 actually pulls away from a BMW M6 (F13) initially so I don't doubt the numbers. However the B7 LCI seems to be a dud especially at $140k against a S8 (which I happened to order btw). I think the weight was the issue not the engine. I doubt we will see the B3 since BMW does not want to risk losing sales to the new M3. Alpina does not have the dealer network to do it alone in the US.
2013 BMW Alpina B7x SWB Alpina Blue, Dinantronics Stage 2 600hp, 612lb/ft
2013 BMW M6 Coupe Brilliant White Met. Akrapovic Evo full titanium, AMS Alpha DPs, Gruppe M intake, HRE S101s 20s, full BMW M perf parts, comp springs sway bars, Dinantronics Stage 2, 713hp 651lb/ft