Is the S5 enough?
For most single-bathroom households, yes. The wash quality is the same as the S7 — what you give up is unlimited warm water and the auto lid.
If the bathroom is used back to back by several people, the S7 is worth the difference. Otherwise the S5 is the better value.
Where the S5 sits
The S5 has the features most people actually use: heated seat, adjustable warm water and pressure, oscillating spray, a warm air dryer and a self-cleaning wand.
The one difference from the S7
The S5 heats water in a tank rather than on demand. That gives roughly 40 seconds of warm water before it needs to reheat, which is fine for one user and can be noticeable with two in succession.