When talking about Ivy v Sandy, Ivy is the more up-to-date architecture but the improvements are generally on the integrated GPU side. They will be slightly better than Sandy for processing, but not a step change...for gaming, you'll not notice the difference, practically speaking.
For overclocking, you add longevity to your system as you can push the CPU harder instead of upgrading to a newer one. It can lead to component failure as you're pushing it harder but CPUs are robust. Just make sure you have good cooling. Due to the 22nm architecture on the 3570K, the temps that it will be at when overclocking will be greater than they would be on the 2500K at the same frequency, which could over time translate to a quicker wear out with Ivy v Sandy. However, you're probably talking 7 years v 7.5 years, which isn't going to bother you if you replace after 5 years.
The 1st build can't be overclocked as it doesn't have an unlocked multiplier like the other two builds you put up, so if you're interested in OCing, don't go for this build.
The 2nd and 3rd builds are good for gaming systems. It just depends on what CPU you want...both are good and both will last a good while. I'd go so far as to say Ivy won't necessarily last longer than Sandy as a gaming CPU despite being a year younger, as from the processing side they're reasonably similar.