I write most of my songs in B or drop A, and I've got an Ibanez BTB that has always done the job just fine. It's not just a 5-string, but an extended scale 5-string, so drop A is nothing. I use TabIt to write all of my music, so I don't actually play it when I write it, so I'm not sure about the string tension until it's time to record. I've written some songs in G standard that translated well to audio, but at drop F, the BTB starts to really bottom out and falter. I found that playing the drop F songs in drop A sounds better anyway.
I bought a G&L 5-string recently, though, so if the G&L can't handle the tuning, I don't use the tuning. That's the rule for me nowadays.. the capabilities of the best-sounding equipment become the limitations.