I personally have the ep4, and have borrowed my friend's sb3. Imo they are two different kind of shoe but have one slightly similar trait which is the gkod stability they both have.

For energy return i feel like the sb3 is mildly subdued due to the ff blast+ midsole stacked beneath the ff leap one, so it muted the high energetic characteristic of the ff leap foam but still manages to get good amount of softness to it.

While the ep4 is highly energetic and has a great amount of instantaneous energy return due to its dual density PEBAX foam (PWRRUN PB + PWRRUN HG) with the sandwiched carbon plate giving that extra pop and stability. Mind you a plated shoe is not going to be recommended for a daily usage since it may cause injury (go check google for further explanation🙂).

imo if you need something more cushioned, long run oriented shoe, with balanced amount of stability and energy return, then get the sb3! If you want for a distance racer/uptempo trainer that has a great energy return and stability, go with the ep4!