I'd recommend an Intel Core i7-990X, but you might need to check for deals on Ebay or something, as that thing might not come cheap (MSRP: $1059). You can also buy a Xeon X5690, i7-980,... But remember to get a good cooler for them, as they are hot as hell when running at full load (130W TDP)
IDK if there are any more 6-core LGA1366 CPUs, and that is my suggestions.