The i7-5930K SR20R is the fastest-clocked Haswell-E part (3.5/3.7GHz, 6 core, 15MB, 4x16GB DDR4-2133, 140W). It is of course a lesser-binned i7-5960X SR20Q with some deactivated bad silicon but which can sustain higher operational speed.
There are also a couple of faster-clocked Haswell-EP parts - E5-1630-3 SR20L (3.7/3.8GHz, 4 core, 10MB, 4x192GB DDR4-1866, 140W) and E5-1680-3 SR20H (3.2/3.8GHz, 8 core, 20MB, 4x192GB DDR4-2133, 140W) - but they're both somewhat difficult for consumers to obtain.
I use an E5-1680-3 SR20H on my main R5E, it's a higher-binned i7-5960X SR20Q die packed with Xeon-grade memory controllers, it can be unlocked and overclocks well enough, and it's probably the most beautiful processor I've ever had in a home computer. If money is not a factor then this is the processor you want on your X99.
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