Like a comment on another thread, 0.25x would be the much better way to say this. It's 25% of the original value. It's also consistent: If 3x means 300% the original value, then 0.25x is 25% of the original value.
If you say 4x lower, that changes the semantics for lower than x vs higher than x, which is absurd.
If you say 4x lower, that changes the semantics for lower than x vs higher than x, which is absurd.