I think you should look at the label of the fiver for the empty weight also. It could be that it is about 12K and has about 4K in cargo capacity. My fiver weighs 10,600 lbs empty and 12,000 ready for camping. It has a 14,000 GVWR, but it will never be that heavy. That's just not what we do, but I know a lot of people load them down.
I think it's certainly wrong to plan using the empty weight, but you can also cost yourself a lot of money just automatically using the GVWR if you never load it that heavy (especially given some fivers have 4-5,000 lbs of cargo capacity). If you know you'll fill it up heavy, use the GVWR. If you know you'll put the same amount of stuff you have in yours now, then how much does your stuff weigh? If you load about half the cargo capacity, then your SRW may do fine. If you are going all the way to GVWR, then I see a dually in your future. Hope this helps. Good luck.