He is not upgrading a 2500k with a 2600k. Read the damn thread bandwagoners.
He is building ANOTHER system and wants to keep the old one with warranty intact. Listen up.
I swear some of you people have a complex over owning a 2500k. Do you need to justify it by bleating on about gaming and how a 2600k is pointless EVERY time someone mentions 2600k? If you can spend whatever you want and are not building to a budget you would always get the 2600k - It's the better chip overall ignoring cost/specific application.
OP - Do you NEED to OC a 2600k, nope. Should you? Yeah, why not. A decent air cooler and you should see 4.5GHz easily with safe temps and voltages.
4.5 is easily achievable as a 24/7 clock and I would suggest you aim for that, out for the box. No need to go further unless you want to bench.