i5 6500 + r7 260x Vs i3 6100 + Gtx 1050 ti



But my resolution is only 720p...wouldn't there be a bottleneck in cpu hungry games like GTA V and ACS ? If it was 1080p then I would get the i3 combo without any doubt....

 
The question is... Is the cpu limitation because you do not have enough threads, enough total cpu power, or enough single thread capability.
Games such as mmo, strategy and sims tend to depend on strong single thread performance.
Multiplayer games want many threads.
Games that can fully utilize all 4 threads are unusual.
Both i3-6100 and i5-6500 have the same number of threads... 4.

For GTAV, the link above
http://www.anandtech.com/show/10543/the-skylake-core-i3-51w-cpu-review-i3-6320-6300-6100-tested/10
tested at 720p shows the I3-6100 slightly better than the i5-6600, a $220 cpu clocked at 3.3
The I5-6500 is a bit slower, at 3.2 and still costs $200.

The i3-6100 excels at single thread performance, it is only when all 4 threads can be fully utilized that a I5 becomes more useful.

Then too is the market positioning of the I5.
At some $200-220, it seems to me that one who wants good cpu capability should pay a bit more for a $230 I5-6600K and overclock it.
You will get some 50% more performance for 10% added cost.

Of course we all have budgets,'
That is where the i3-6100 comes in at $125.