Not sure what to upgrade between CPU/motherboard and GPU

Kryne

Honorable
May 8, 2013
20
0
10,510
What I have

Asus Crosshair IV Formula AM3 890FX
AMD Phenom II X4 955 Black Edition Deneb 3.2GHz Socket AM3 (overclocked @ 3.7GHz)
SAPPHIRE 100314SR Radeon HD 6870 1GB 256-bit GDDR5 PCI Express 2.1 x16
Cooler Master Hyper 212 EVO

Here was my current plan.
Upgrade CPU and mobo to 4th gen i5 ($220) and a new mobo ($120). Then the GPU probably around Christmas time, would most likely get a GTX 660 Ti or 7950/7870. I would potentially upgrade sooner if I can sell my current CPU/mobo for around $150 or more.
Now I'm not sure. Is that the right path? Is my GPU still good enough for awhile or should I upgrade that first? The CPU/mobo combo is going to be more expensive ($370 or so) and I have that money currently. If I upgrade the GPU first will it be bottle necked by my current setup.
Thanks in advance!