In lieu of the 17.5 wheels, you could look at a G-rated 16" tire such as the Goodyear G614 RST that's rated at 3750 lbs @ 110 PSIG. It would have adequate capacity for your 7K axles. Be sure the 16" wheels are rated for this weight and pressure. Someone will be along with a recommendation for a Sailun "equivalent" for the G614, I'm sure. I'm just not familiar enough with the Sailuns to make a suggestion.
I'm not against the 17.5" tires and wheels; I've used them myself on 7K axles on a previous 5th wheel. It's just worth considering whether you want to spend the money to get 4805 lb @ 120 PSIG tires on an axle that's limited to 7000 lbs when there are less expensive 16" alternatives. It's your money and your choice.
Rusty