I would rather give away my right arm. I imagine if I posted a similar question asking whether I should give my children away I would be shot down in flames, but that's how I feel when I read about people giving away their pets "for the good of the pet". I apologise if I sound judgemental, but sadly in the current "crisis" there are so many stories of ex-pats leaving Spain and dumping their pets because they say they cannot take them home with them. Obviously your circumstances are slightly different, but even so, please do not listen to those people advising you to give Moggie away. If you are concerned about how he will cope with the travel and foreign climate, maybe the good people at the cattery would agree to look after him for the 4 months, but when you return, surely you would regret it if you couldn't go get him to bring him home?
If you do decide to bring him with you, do make sure (sorry if this sounds obvious) that he is fully vaccinated, chipped, rabies jabs up to date with blood tests etc. etc. and that you know what you have to do on the return leg. All the info is available online or from your vet. And finally, I'd just like to say that if he does come with you, please make sure that he cannot get out of your garden and go walkabout, and that he doesn't come into contact with any of the natives. FIV is rife amongst the many feral cats in Spain, and the last thing you want is for him to come home with an unwanted souvenir.