Sometimes this can give troubles by thinking which one you will choose. We know there can be were tight cases when you are facing a certain pokemon. At this time Charizard mostly needs last 3 stats (Spakt, Spdef, Spd). I had same issue long ago. I was testing them both for a while. Soon as he can kill Slahking he is fine also I am not sure would that 1st one OhKO some Venusaurs, Meganiums etc. But thing is Feraligatr will not OhnKO 1st one though. Sometimes you could be in situation when he needs to sustain a hydro pump launched from Feraligatr and smaller spakt based Lapras, Swampert etc in order to strike with 2 hits. You can left with 1 HP point before facing Venusaur, it would not be nice if Venusaur survives.
-Best thing is to test them out against nice stats earlier listed Pokemons. Also I would test him against other Charizard just in case, for example that second one VS first one. I saw many times when slower Charizard kills faster one. For example +29 IV Spakt could give a trouble for that lower Spdef one.
As (Hp, Atk, Def) concerns no Charizard will faint from STAB based normal/dragon etc. in 1 hit.
But yes I would go for a second one for sure since not everyone has a perfect Pokemon that will counter him. Charizard is only used to kill in 1 blow mostly and to kill Slahkings.