No, 8th-gen Intel requires a 300 series chipset. As of now Z370 is the only chipset that supports 8th-gen Intel. You can use a 7th-gen Intel CPU with your B250 motherboard. With a 200 series chipset motherboard, (in my opinion) an i7-7700(K) is the only real upgrade from any 6th or 7th-gen CPU if you have at least a Pentium G4560 or above.
i5-8400 is on par with the i7-7700[strike](K)[/strike] in gaming.