I would go with the core i5-2500k and re-use the HD 4850. It is no longer considered high end, but it's still pretty good. Then when you save up enough money, upgrade the video card.
Many gamers upgrade the video card a few times before upgrading the entire PC so instead of eventually upgrading the CPU and the GPU, just focus on locking in a good CPU now, then worry about the GPU later.
Yeah, a 2500K will solve all your CPU worries for a long time AND you'll be able to overclock the crap out of it if you ever want even more power. You're basically getting something you probably won't need to upgrade for the lifetime of your rig. If you get a top-end GPU NOW with an i3, you'll be looking to upgrade BOTH in two years.