Upgrading my CPU and motherboard for $300-$400

Got a ton of great assistance when I first put my current setup together, now looking to upgrade given the holidays are coming up. Here is my current Mobo/CPU combo.

ASUS M4A88T-M/USB3
AMD Phenom II X6 1055T Thuban 2.8GHz Socket AM3 125W Six-Core

All I'm really looking for is a new CPU, but in order to upgrade I was wondering if I might end up needing a new MOBO. My range is about 300-400 dollars... so is there any way I can get a new setup going with that much money? Maybe just upgrade the cpu? Am I being a little too optimistic? Thanks for any help!

What are you using the PC for? Unless your CPU usage is maxing out frequently and you know you need the extra CPU power, I wouldn't really bother. The only thing worth upgrading to is an i7 3770K which will cost quite a bit.

A cheaper and probably better solution is to get an aftermarket cooler and overclock your CPU (if you haven't done so already), the Phenom II's OC quite well.

Its seems to me that a 3570k would still be an upgrade to this cpu in gaming power and more. overclock to around 4.5ghz hard to compete with.

http://www.newegg.com/Product/Product.aspx?Item=N82E16819116504 Intel i5-3570k
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128546 Motherboard lga 1155

215$
135.99$
350.99$

Total and a great Overclocker and Multitasking +gaming

The motherboard was just a pick of my choice neweeg has all kind of Mobos if u want for crossfire Sli or Massive Overclocking just leave us a specification of what u really want this upgrade for