I do not think 5 fpe is enough. I shot one squirrel with about that energy and it took it several days to die. It was hit solidly on the shoulder and broke it but did not penetrate into the chest. It could not climb a tree but could run well. I couldn't get another shot on it and found it several days later dead in the yard. If I had hit it in the head I would probably have had a different result. But my shot was well placed and the animal took days to die. To me, risking that just to use a 5 fpe gun is not OK. I have not shot that gun at a squirrel since.
I realize that is not the main dialogue point here, it is 11-12 fpe guns. The closest I have had to this was my Prod before I tuned it up to 17-18 fpe. Stock it was 13-14 fpe and after shooting 4 squirrels with it at that power level I thought it was a bit weak. I tested penetration on a dead one and the 14.? grain pellets I was using would not shoot through at 25 yards. They would shoot through the shoulder and get to the vitals but I decided I wanted more power. I got it and the 11 after that were DRT. I will freely admit there is a good chance my early issues were likely at least contributed to by worse shot placement than my final 11. Head shots were never an issue. Prod is a 22, of course, and penetration would be better with a 177 as would trajectory. That's why I think a 177 is a better choice if you have to stay at 12 fpe or less.
Trajectory is a good bit of the reason I like my airguns to have a bit higher fpe. It is easier to properly place the pellet with more velocity and thus energy. When they will do it, I tune my guns to shoot 800-900 fps with pellets they like. That is why I have a 19 fpe 177, a 32 fpe 22, and a 32 fpe 25. The 25 likes H&N FTTs which are lighter than the Baracuda Match the 22 likes so they have almost exactly the same fpe. I'm sure that 32 fpe isn't necessary but it works great in the 25 and I think it will in the 22 too. I'm waiting for some squirrels to volunteer to test this theory.
All my guns are sighted to give me a 1/4 inch mid trajectory rise. My logic is I can ignore the 1/4 inch on squirrels. My ~750 fps Prod thus has a significantly closer zero point than my 900 fps P35-177. But both are close enough at 25 yards, my most typical shot distance, I do not have to hold over or under. The guns which will do over 800 fps are zero'd close to 40 yards. So they are within 1/4 inch from about 20 yards to over 40 yards. The occasional under 20 yard shot is more of an issue for me than over 40. I'm practicing on sparrows to get better at those close shots.