I have had one cab with the 3015 and you could really hammer it with out farting out. when it comes to any speaker if the cab is not ported or tuned properly you can have a lot of problems. The main reason I didn't go with the 3015 is the nasty frequency bump between 1 and 3k. I wanted single 15's and that was it.
I have messed with a few cabs and win-isd and have come to a happy place with these Faital pro speakers. I have pushed one and a pair pretty hard with 5 strings with no problems except maybe the strong breeze that comes from the speaker ports.
Now I certainly don't have near the knowledge of several people on this web site but to me, my band mates and several sound people I have worked with they all love my cabs. Maybe it because they look beat up but they've got it where it counts.
Were I in your shoes I'd measure my cabs, download win isd and plug in some speakers to see what you come up with.
You can call the guys at US Speaker too. They're pretty helpful.
Thanks for the info. I hope I can figure something out before I end up selling all this stuff and buying off the shelf. Dang..