Quite significant in theory, DDR3 maxes out at about 2000 MT/s (mega transfer per seconds) while DDR5 can go above 8000 MT/s, so about 3x-4x. I don’t know if this metric already includes the capability of DDR ram to access multiple data in a clock cycle, but I think it does. If it doesn’t, tje difference is even higher.

Of course in practice the difference is not as remarkable, but still noticeable. Still, DDR3 is perfectly usable with a decent processor (light gaming and professional software), my main righ is a 4th generation i7 and I have no intention in upgrading for the foreseeable future.