Ivy Bridge is, at max, 55% faster in IPC than PD going from memory.
If you quote Ivy Bridge as 50% faster than Piledriver - 100% (base) + 50% (improvement) = 150%.
Then if you call Haswell 10% faster than Ivy Bridge (it's more or less, depending on application) you're doing 150*1.05, not 100*1.05 - so your result is that Haswell has 165% of the IPC of Piledriver, not 160% (arbitrary numbers, but pretty close)
50 or 60 percent for Haswell over Piledriver clock for clock is completely reasonable thusly, especially considering PD will be clocked like 200-400mhz above
^just read rest of post, yea
The IPC an AMD CPU offers now is enough for >95% of games out there if you're using a single GPU.
Depending on your point of view, the singlethreaded performance of Piledriver ranges from a slight annoyance to a crippling hindrance. The result is Intel holding a 50% or more lead in some performance starved games, while not really losing any benchmarks with i7. If you happen to play those games and seek performance, it would be silly to get FX. If you don't play any of them or care about singlethreaded performance, you can pocket your saved money and be within a few hairs of i5/i7.
As someone who prefers high framerates to graphical effects, i've found myself being unable to satisfy myself with performance recently in many of the games i played, long time sc2 player, was thinking of buying rome 2 with some friends, meanwhile looking at Natural Selection 2.. Friend of mine spent like $200 on Planetside 2, i played gw2 for a few hundred hours, and now in bf4 beta, a lot of my frametimes were far worse than what i wanted. On 720p low settings, quite a few frames longer than 15-20ms, as much as 3-5% of them slower than 16.7ms (slow enough to miss a 60hz refresh) so i'm more inclined to get the best CPU available (4770k or 4930k, depending on the game) even if it costs extra, rather than saving money on something that is "good enough" for "most" applications. I do like the FX design though and if Steamroller is close enough in singlethreaded performance to not get completely destroyed in some of my favourite games (or lets be honest, if engine development standards improve) then it will be a very interesting fight!