The primary differences between mobile Core i3 and i5 is:
1. The Core i5 has slightly higher base clock speed. Excluding CPUs meant for ultrabook 3rd gen Core i3 CPUs ranges between 2.4GHz to 2.6GHz depending on the model. Again, excluding ultrabook CPUs, Core i5 CPUs ranges between 2.5GHz to 2.9GHz depending on the model #.
2. The bigger difference is that Core i5 CPUs has Turbo Boost which automatically increases the clockspeed when the CPU is stressed; as long as it is not too hot. With Turbo Boost the max clockspeed ranges between 3.1GHz and 3.6GHz depending on the model #.
For example, the i5-3210m has a base clockspeed of 2.5GHz. When Turbo Boost kicks in the clockspeed can reach up to 3.1GHz if only one core is being used or about 2.9GHz when both cores are used.
In general, for a gaming laptop, if you had a choice between #1) a stronger CPU with a weaker GPU, or #2) a weaker CPU with a stronger GPU, then you want to go with #2. Of the three laptops you listed, you want option 3.