Here is some benchmark result that compares the integrated graphics in the Ivy Bridge ( HD Graphics 4000) Vs the discrete graphics - Nvidia GT 520M. According to the benchmarks, the HD Graphics turn out to be slightly better that the GT 520M discrete graphics. Here is the benchmark result.
The graphics 4000 is about 9% faster than the 3DMark 05. This could be a good reason to go for the Intel. Of course, the Trinity APU from AMD that launches in June will have even better graphics performance. If low cost decent quality gaming is your aim, wait for Trinity.