Neither of the above are ideally suited to gaming. The on-board option may appear to have more memory, but chances are that this is shared system memory not dedicated SGRAM.
The G450 is a good general purpose card and should compare reasonably well to the on-board option, but is was designed more for office productivity than gaming. It's 2D performace was leading edge in its day, but 3D was never anything special.
I suggest you post back with a few names of games you are intersted in running, and we will be able to give you some idea of the amount of grunt required.
Also post your basic system specs (cpu/ram/HDD etc)
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