Could anyone advise if the dell Alienware Area-51 with Dual GTX 980 Ti (NVIDIA SLI Enabled), will do for this job well? Any other readymade solution someone could buy?
Wouldn't recommend alienware at all, it's for gaming, not hashcracking, and you could make way cheaper gaming pc by yourself.
Some companies make "readymade" solutions (https://sagitta.pw/hardware/ for example).