The 1st number in all of those models represents the generation of cpu. Thus the 3470 is the third generation, 6500 is 6th and 7600 is the 7th generation.
Thus 7600 is newer then 6500 (and hence marginally better), and 6500 is 3 generations newer then a 3470.
Now if you say already had a 3470 then this is still a very usable CPU, it wont support the best of the best GPUs like a 1080 or Titan but it will support pretty much anything under that.
Now the 3470 uses a completely different (older) socket (that means how many physical metal pins interconnect the cpu and motherboard) then the 6500 and 7600 does. Finding a new 3470 and supporting motherboard is not going to be possible.
The 7600 is brand new (like released last month) and so finding supporting parts and motherboards may be difficult in your country.
Thus my suggestion is to get the i5 6500 and a supporting LGA1151 motheboard. Motherboard chipsets that support the 6500 are h110, b150, h170 and z170 so look for boards that have one of those chipsets on them.
You will also need new DDR4 memory for your new motherboard.