The Geforce 750Ti won't give very high fps with Battlefield 4.
https://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-9.html
About 36 fps at 1080p
$60 for an i5-6600 is a great deal, about 70% off normal price of about $200.
Just don't forget you still need to buy ram and a motherboard at a "normal" price which would eat away at the 70% off.
For example if the
motherboard was $100
ram was $130
cpu was $200
that gives a total cost of $430.
But with your cheap cpu
motherboard was $100
ram was $130
cpu was $60
that gives a total cost of $290 or about a 33% dollar savings with the motherboard and ram included.
You save about $140, but the percentage saved decreases with every part you buy at full price.
The percentage sinks ever further if you need to include the power supply and case.
Only you can decide if saving $140 is worth choosing a cpu that is 3 generations behind.
Personally if I had to build a computer at a similiar price point I would build it around a RYZEN 5 2400G which go for $160.
It's $100 more than the price for your i5-6600, but is much more powerful with its 8 threads and the same 3.9Ghz turbo speed.