That's a very difficult question. normal sizing is when you know applications size, num concurent users and increase the data in the application for a period of time.
the initial stages of the first server will be better because a higher frequency
but Xeon E5 2600 Famaly is the recommended processor. and this platform will be more scalable.
regarding the disk subsystem - click is not demanding of her speed. More important is the amount of RAM. The bigger, the better.
look to Intel® Xeon® Processor E5-2643 v4 (20M Cache, 3.40 GHz) Спецификации
This CPU will be better for Qlik then 2620v4 and not particularly expensive