Yes it would be a worthy upgrade both for amount and speed..... though i think you will find barely any price difference between DDr3-1600 and DDr3-1866 or even in many cases DDR3-2133. look for the lowest time in nanaseconds which can be calculated from CAS and speed. For example:
CAS Timings ....... CAS/ Speed x 1000 = nanoseconds (voltage)
Cosair Vengeance Pro
9-9-9-24.........9/1600 x 1000 = 5.63 (1.50)
9-10-9-27........9/1866 x 1000 = 4.82 (1.50)
11-11-11-27.....11/2133 x 1000 = 5.16 (1.50)
Corsai5 Dominator Platinuim
9-9-9-24.........9/1600 x 1000 = 5.63 (1.50)
9-10-9-27........9/1866 x 1000 = 4.82 (1.50)
9-11-11-31.......9/2133 x 1000 = 4.21 (1.65)
Mushkin Redline
8-8-8-24.........8/1600 x 1000 = 5.00 (1.50)
9-9-9-27.........9/1866 x 1000 = 4.82 (1.50)
9-11-11-28 ..... 9/2133 x 1000 = 4.21 (1.65)
Out of the above, the 4.21 is the fastest. As for voltage, don't shy away from 1.65 but if the same speed and timings are available......the lower voltages will reduce the load on ya memory controller to a minor extent
I use the Mushkin 997121Rs which won the performance races in THGs test below
http://www.tomshardware.com/reviews/memory-scaling-gaming-haswell-richland,3593-18.html
The G.Skill’s DDR3-1866 CAS 10 came in as the value conscious purchase.