Yes atm there aren't very many applications that make great use of high speed memory, except GPU based ones, so my advice would be to go for something that's cheaper i.e. 2400MHz in this case. In the next year or two you will get mem that'll exceed 4000MHz & be twice in capacity, probably at the same price that low end DDR4 kits cost today. I'd wait till then to upgrade, at the very least you either wait for capacity to double or mem speed to (nearly) doubly & that's what I'd do.