Ya, but this thread isn't about i7 6700K Skylake vs. i5 2500K. As I already mentioned before you missed my post - Watch Dogs runs like garbage on almost everything besides higher end cards like the 980Ti. You then proceeded to post a bunch of benchmarks with a 980Ti which doesn't apply to the OP so what was the point of that? Are you trying to suggest that if we maxed out graphics sliders and then averaged the FPS in the
entire game from start to finish in GTA V, The Witcher 3, Watch Dogs that an i5 2500K @ 4.5Ghz with a 980Ti @ 1.5Ghz would destroy an i7 6700K @ 4.8Ghz with an R9 270X CF @1440P? Even if you drop a 290/970 in there, 980Ti OC will still easily. Ya, sure I can find spots where there are dips but similarly a 980Ti OC is as fast as 970 SLI and there are many games that are going to be GPU limited by far.
Will a faster CPU improve the OP's performance? Of course, but the OP first had 6950s CF in his sig and now has 2x270X CF, GPUs still well below a GTX980Ti. There is no way he should be upgrading his CPU platform if the choice is CPU vs. GPU, when he would be better off grabbing a
$235 R9 390 (selling off those 270Xs) or going all the way up to a 980Ti. You can link 10 games where the i7 4770K/6700K destroys an i5 2500K in minimum FPS and I'll link 95 games at 1440P where a 980Ti with an i5 2500K @ 4.5Ghz would wipe the floor with an i7 6700K @ 4.8Ghz and a GTX970. That's the point. It's about balance and budgets.
I mean what if the OP doesn't play Watch Dogs or Crysis 3 or GTA V? In that case, that's 3 major games that have issues with an i5 that are completely out of the picture. What about 95% of all PC games that would benefit greatly from the 390 or 980Ti over his 270Xs?
Also, the OP can also consider grabbing a used 2600K and that provides a major boost in some of those games you mentioned earlier.
Trying to turn the entire thread to point out that a 2500K @ 4.5Ghz is a bottleneck misses the entire point of this thread. Every single components in any PC is a limiting component - the question is which one is the most limiting, not whether a particular CPU or GPU is limiting performance.
Just imagine so many other games where an i5 2500K @ 4.5Ghz with a 980Ti would absolutely crush an i7 4770K/6700K @ 4.8Ghz with any lesser GPU - there are going to be 100s of those games. Unless the OP can afford both a platform upgrade + a $600 GPU upgrade, using a handful of games to show that a 2500K is a major bottleneck is just stating the obvious but it doesn't get to the bottom of the main issue here -- 270Xs CF @ 1440P gaming are BY FAR the bigger bottleneck, not his 2500K OC.
You seem to be overly sensitive to FPS drops as you noted before you MUST have 60 fps VSYNCed at all times. Since the OP was using HD6950s @ 1080P/1440P and now R9 270Xs in CF, he automatically doesn't even fall into your must have at least 60 fps minimums at all times standards. For someone like him, upgrading his GPU and possibly substituting the 2500K to a 2600K is the way to go. Moving from an i5 2500K OC to an i7 6700K while keeping R9 270Xs for 1440P is just $ wasted.
Look at the title of the thread again.
"2500k @ 4.5GHz (Any need to upgrade?)"
The OP has R9 270X CF and has states that he plays up to 1440P. The answer is a definitive NO. Unless the OP gets a much faster GPU such as R9 390 or even 980Ti, he should not upgrade his CPU.