Replacing coil packs

[Como]

Anyone know when is a good time to replace these? Is it by feel? Mileage?
I know from experience old GM v6's with their coil packs they would work fine, then next time you hop in, your car won't start. Also had Chevy small blocks with coil and distributor and coil still working but would sputter on wot. Just weak spark (quite hard to spot).
First time I've dealt with this type of system with coil on plug. Do they just completely die suddenly? Or slowly fade out?
Thanks
Sometimes feel my car hesitates or uneven acceleration. My TB clean and plus less than 1yr (gapped iridiums).

[peterm15]

When they no longer work.

[silverstarmazda]

When you get a contant misfire or a dead cicylnder could be the coil. Another thing is to just pull them out and visually check them over all. If your anal about the efficientcy of the coil pack, you could test it with a volt meter.

The coil pack isn't an overly worn item, so they should last a long time if everything is working correctly