I am thinking about getting a i5 2500k with a future build for ivy bridge. But after reading that the ivy bridge won't be a huge difference against the sandy bridge, should i cut down on the cost of making it future ready and just have it sandy bridge ready.
I'm thinking about getting a only USB 2.0 case with only USB 2.0 motherboard features. No PCI 3.0 slots, instead i will only have PCI 2.0 slots.
I've heard that the i5 2500k could lasts up to 10 years before upgrading again. So there is no point in making a i5 2500k build that will be future ready for ivy bridge. Because by the time the 9th or 10th year comes around, there could be something that is better than ivy bridge.
IMO this depends a little on how future games are programmed and whether developers start threading more heavily. The i5 2500k is quad core and can run 4 threads, and right now its gaming performance is basically the same as the i7 2600k (which is quad core but can run 8 threads due to hyperthreading). In games the 2600k is basically identical to the 2500k because each core is basically no faster, and games are not heavily threaded now.
It seems unlikely that on a per core basis there will be a lot of improvement over the i5 2500k any time soon, especially an overclocked i5 2500k to 4.5 or 5 GHz as is typical. So as long as you're sticking with gaming, and as long as games don't become heavily threaded any time soon, you're fine skipping ivy bridge. (This is all just a guess.)
Technology changes so often I doubt you'll want to keep a PC for 10 years so build it to last 5 years with minor upgrade options if you play games. It will last longer if you don't need gaming performance. As for your other choices I think most MB's come with USB 3.0 so I wouldn't pick a USB 2.0 specific board and stick with PCiE 2.0 slots unless the board you like has PCiE 3.0 slots. Ivy bridge should perform 15-20% better than Sandy Bridge but that's to be seen. If you don't need a PC now wait 6 months and Ivy Bridge will be out.
I don't see how Z68 offers any "real" upgrade route that you'd be constricted by. I remember having the same worries in the 286 days when we all worried about waiting for 386 compatible MoBos so we could upgrade when the 386 came out ..... repeated that worry with each successive generation and 200 builds later, only once did I do a CPU upgrade and that was from a P300 to a P600 when I wanted a P600 and a frond asked me to build his P300 .... I bought a P600 and gave him my P300 .... That P600 is still running in my office 24/7 on an Asus P2B-S SCSI system.
If you are gonna wait 6 months for the next best thing you will never buy anything as the next best thing after that is just 6 months away. And yes, I have a system in the office running for 10 years but it's been retired and an AutoCAD box and turned into a file server....I don't do any actual work on it. It is still a very fast machine but it's fast using 10 year old OS and software. It would not run today's OS nor today's AutoCAD.
In short, ten years is a bit much, a gaming box can get by for 3 or 4 years ..... meybe even 5 but at the 4 year point it's gotta be relegated to 2nd class status .... unable to run the latest and greatest.
I think this comes down to the specifics... what is the cost difference between the case and mobo with everything else you want but not the "future ready", vs. the one that is also "future ready?" And if you didn't spend this money on "future ready", what would you spend it on instead?