Well I started with a 2x16 2666 kit that managed 3200 CL14 but wanted better, I was able to sell it for £130 and buy a 3200 kit for £150 that turned out to be Micron E Die which is still running at 4200 CL16 1.55v.
I think that was well worth the £20, but I got super lucky with getting an E die kit at that price.
Its only worth it if you can get a guaranteed Micron E die of Samsung B die kit for not too much more.