Does it matter? Will one hold up better than the other outside where its about 90 degrees? It will be on a carved cake covered in fondant. Should I keep the cake in the refridgerator until she picks it up to help keep it from melting, ot will it sweat really bad? The party is outside and she likes to show off her cakes. Last year she got a sandcastle cake that melted & fell apart so no one got to see it when it looked good. Any suggestions, my fellow cake buddies & gurus?

Indybebi's recipe says it holds up in 90 deg for 5 hrs, it uses crsico

WOW......I would say keep it inside........if you refrigerate it and then take it into heat it will sweat for sure.....between the two.....butter may be worse in heat........either can't be good though for a long time.....but yeah I agree butter may be worse

Under the fondant or on top? You don't have to substitute butter for crisco, because you trade good taste for bad also , just try 3/1 butter/crisco, last time i piped it on cupcakes, ot holds pretty good, bur it was inside, under the sun even crisco wil melt ...
So try 125 g crisco and the rest butter in your recipe, I think I got it from Toba Garrett's site, holds good autside the fridge.