How big a difference between DDR3 1066 and DDR3 2133

As said to a degree, it depends on other factors like your CPU and MOBO - mostly your CPU. Next, it depends on 'what' you want to make 'faster' and specifically what applications. The trade-off even with LGA 2011 is a degree of stability.

Personally, the only options today with DDR3-2133 are the SB (K), SB-E, and FX CPUs. Even the AMD AM3 6-cores can barely handle >DDR3-2000 with an OC, and the non-K on the P67/Z68 (only certain SB chipsets allow >DDR3-1333) it isn't recommended.

Further, keep in mind RAM's speed is a factor of both its' Frequency and CAS Timings. IF the CAS Timings are too high then heck a ultra-low kit of DDR3-1600 can be 'faster'. Frequency is the 'transmission', CAS Latency the 'stops', and CPU the 'governor.'

Here's a good article for SB LGA 1155 and RAM -> http://www.bit-tech.net/hardware/memory/2011/01/11/the-...