lets think logically for a second here

an 8 core chip with just 4 cores running gets up to 4.2ghz
a 4 core chip with all 4 cores running also gets 4.2ghz, when its just 2 less its able to get an extra 100mhz due to not having to power additional L3 and crap

so i think the numbers do make sense (when thinking about peak power draw for different chips) and we have seen amd offer really fast lower clocked cpus, but i dont think they would want to hurt their higher chips sales by making the cheaper ones win in some/alot of benchmarks.