If you want to be on the safe side then go ahead and get the 4690k and overclock it when you need it. OCing the CPU typically only require tweaking the CPU voltage and setting the ram speed to its specs. If you're an adventurous then you can play around with the more advanced settings.
[color=#3366ff]CPU: Intel Core i7 4790K OC'ed @ 5GHz[/color]
[color=#339933]GPU: MSi N580 Lightning Extreme 3GB[/color]
[color=#cc3333]RAM: CORSAIR Vengeance Pro 16GB DDR3 @ 2666MHz[/color]
[color=#333333]HDD: Samsung 840 Pro SSD 512GB[/color]
[color=#6666ff]CPU cooler: Noctua NH-U14S w/Noctua NF-A15 PWM 140mm Premium[/color]
[color=#ff3333]MOBO: Asus Maximus VI Hero LGA 1150 Z87[/color]
[color=#cc3399]CASE: Thermaltake Urban T81 Full Tower[/color]
[color=#339933]GPU: MSi N580 Lightning Extreme 3GB[/color]
[color=#cc3333]RAM: CORSAIR Vengeance Pro 16GB DDR3 @ 2666MHz[/color]
[color=#333333]HDD: Samsung 840 Pro SSD 512GB[/color]
[color=#6666ff]CPU cooler: Noctua NH-U14S w/Noctua NF-A15 PWM 140mm Premium[/color]
[color=#ff3333]MOBO: Asus Maximus VI Hero LGA 1150 Z87[/color]
[color=#cc3399]CASE: Thermaltake Urban T81 Full Tower[/color]