I7 QUAD VERSES HASWELL ON 15" MAC PRO RETINA

Question

I'm looking at these 2 configs. What is the difference & if I do buy (price is no problem,sped is essential) what do you all recommend?

Answer 1

Haswell is an umbrella term encompassing all fourth-generation Intel Core processor.  All of the options you can get on the current Macbook Pro are Haswell, and all of them on the 15" model are quad-core i7 (the 13" models are all dual-core, some i5 and some i7).
According to Apple's tech specs page, on the 15" models, there are three processor options:
2.0GHz quad-core Intel Core i7 (Turbo Boost up to 3.2GHz) with 6MB shared L3 cache
2.3GHz quad-core Intel Core i7 (Turbo Boost up to 3.5GHz) with 6MB shared L3 cache
2.6GHz quad-core Intel Core i7 (Turbo Boost up to 3.8GHz) with 6MB shared L3 cache
All of the 15" models come with Intel Iris Pro 5200 graphics.  The two higher options also include a discrete nVidia GeForce GT 750M graphics card.
Given that information, we can use Intel's list of 4th generation Core i7 mobile processors to determine the part numbers.  From there, we see that there are four such processors with the Iris Pro 5200 graphics, and three of them match up with the Turbo Boost clock rates given by Apple's specs:
3.2GHz: Core i7-4750HQ
3.5GHz: Core i7-4850HQ
3.8GHz: Core i7-4960HQ
You can see for yourself on the linked specs pages, but these chips are nearly identical except for the clock rates.
All three chips are very fast.  All have four cores and use HyperThreading to run two threads on each core, so your system will behave as if it has eight processor cores.  You get all of that in the base 15" Macbook Pro for $2000.  For $600 more, you get a processor about 10% faster, twice as much memory, twice as much solid state storage, and the discrete nVidia graphics.  The additional RAM and discrete graphics will have performance benefits for some workloads and not for others; the additional storage is just that; there's no performance benefit to be had there.  For another $200, you can upgrade to an even faster processor, another 8% or so increase in ideal conditions.  If performance is truly critical and price is no object, I think that it probably makes sense for to choose the $2600 config and add the processor upgrdae.
That said, if you don't necessarily need a laptop, the recently announced Mac Pro offers significantly more performance on the desktop.
If you share more about the sort of work you're doing, it might be possible to give a better recommendation.
Have a great day!