A faster card may help somewhat, but probably not dramatically.

Your S4500 will only get the full benefit of a UHS-I card if the camera itself supports UHS-I. If it doesn’t, the card will still work, but performance will be limited by the camera’s interface. Even so, some faster Class 10/UHS-I cards can still be a bit quicker in real use than a basic Class 6 card.

The bigger limit is often the camera’s internal buffer and write speed. In burst modes like Top 20/40, the camera fills its buffer first, then takes time to write those JPEGs to the card. That means card speed matters, but the camera may still be the main bottleneck.

So: upgrading from Class 6 to a good Class 10 or UHS-I card is reasonable and may reduce the wait a little, but don’t expect a huge change if the camera itself is the limiting factor.

A practical workaround is to shoot shorter bursts, then pause briefly to let the buffer clear, rather than filling the full 20/40-shot burst every time.