There aren't any 6 cores out on the 1155 socket yet, but there surely will be when Ivy Bridge starts rolling out sometime in 2012. Btw since it seems like you're unaware, a socket isn't like a component or anything, it's just the type of CPU your motherboard supports. For example 1336 sockets support older chips like the 990x, 980x, 975, 920, etc. 1155 supports the 2500k and 2600k (among other chips, but those are the flagship chips)
1155 is newer, more expandable (Ivy Bridge will be using the 1155 socket) and the prices are WAY better. 2600k isn't far off of the 990x in terms of performance (even does better in some scenarios, usually within a 5% margin one way or the other) and the 2600k is like 30% of the price of the 990x. That and you just have so much more available on the Z68 chipset like SRT, iGPU for faster video encoding, etc. The only thing that would even come close to being a deal breaker for me is the fact X58 can use triple channel RAM, but personally that isn't enough of an incentive for me with all the pros of the 1155 socket considered. Not to mention the fact that Sandy Bridge overclocks SO well in comparison to anything we've seen in the past. It's nothing to hit 5GHz on air with Sandy Bridge.
Btw, more cores does not = more performance. There are VERY few programs out that can even take advantage of 6 physical cores tbh, most programs aren't even optimized for 4 cores yet.