This has been discussed couple of times. Search for it.
Anyway, my understanding is. If the car hasn't been running synthetic since day 1, u should not switch to syn because it WILL be burn by engine ('cuz engine is not used to it). Civic and such should not be switching to syn IMO regardless, go "synthetic blend" if you really want to go with syn. But syn is only be used on powerful engines which comes with recomendations of using syn (and being used since day 1).
You can somewhat safely switch from syn to regular most of the time.
Anyway, the only true most way to find out what is best for you? Try them!
Try syn only oil at next oil change and see how car runs and keep an eye on the oil level. Then switch to blend ...
Let us know, how it went