Update operatives. Slany choice

Plans to buy a DDR3 RAM of 2 laths on 8. But soon will need to change all the hardware, including the CPU, but under DDR3 processors is not much, often caught DDR3L and DDR4, and DDR3 modules are available only on order(have to wait 1-2 days). Does it make sense to take now DDR3 and then Supplement it with under the appropriate processor or is it better just to take norms percent and operative DDR4?