At your budget the best option is AMD Phenom II X4 960T Zosma around 6.6 to 7K. It is not same as the Phenom II X4 processors like 955 or 965. It is basically a Thuban Processor (AMD Phenom II X6 with Turbo Boost) with two cores disabled. So it will offer you Turbo Boost feature. The best thing is that there is a high chance of unlocking it to a full 6 core processor 1065T. Your motherboard does have core unlocking feature, known as ACC or advanced Clock Calibration. In your mobo's BIOS menu just set it to auto and if there are any hidden cores in the CPU, they will be unlocked.