I do not think overclocking voids it as long as you stay within all the limits of the cpu, but I could be wrong. I can say out of all the cpu's I have had; I have not had 1 fail from overclocking, ever. I think the only way you would fry a cpu is if you go extreme with voltages or if you do not keep an eye on your temps.
For 4ghz range should be fairly easy with the cpu's you have listed. Just make sure you use good aftermarket coolers or h2o.

as far as oem; Origin is correct; only difference is warranty and HSF

also make sure you use a good thermal paste. everyone here has their own opinions. I like arctic silver 5 or IC diamond