What FPS will I get in CrossFire with these computer specs?

AMD Athlon II Dual Core Processor
Processor Speed: 2.2 GHz
RAM: 4 GB

Hard Drive Capacity: 640 GB
Graphics Chipset: ATI Radeon HD4250
Integrated Video Memory: Yes
Native Screen Resolution: 1366 x 768
Upgradable Video System: No
Video Memory" 1789 MB

Pre-loaded Operating System Windows 7 Home Premium

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Its a Toshiba 14" Laptop that I am planning to buy. Around what FPS will I get in CrossFire with these specs in 1v1 and 8v8s?

EDIT: Also I will run Gamebooster 2 and lower the game settings and resolution to get a higher fps.