I have an ARB bull bar (say +90 lbs over stock), XD9000 winch with synthetic line (call it 65 lbs), two PC1400 batteries in place of the original group 27 (say +35 lbs over stock) and bolt-on Mobtown sliders (I dunno, 100 lbs for the pair?).
So call it about 240 lbs over stock on the front axle, 190 lbs hung in front of it and 50 lbs behind (assuming the sliders are about centered between axles). With this I feel the 650# is about right. My springs are compressed to approximately 10.5" (3.5" compression) on the driver's and 10.875" (3.125" compression) on passenger. That represents 2,275 lbs on driver and 2,031 lbs on passenger. Which is about right when you figure the fuel tank and batteries are on that side.
A 700 lb/in spring would change these static numbers by 0.25", but the difference is that it will travel dynamically that same ~7% less on a pound-for-pound basis. At block height of 6.61" my King spring will hold 4,804 lbs and the old 13"/600# Eibach/FOX would hold 4,350 lbs fully compressed. A 700 lb/in, 14" long coil should hold about 5,200 lbs at full compression.
In my use (not high speed desert) it's unusual that either would bind but I feel the extra 500 lbs margin is nice to have and the ride isn't mushy nor rattle fillings loose firm. I do get some body lean on two-lane but I don't feel the need for a sway bar (mine's long gone).
For comparison OME recommends for a bull bar and winch (they assume 200 lbs) to use their x886 spring to achieve 2.75" of lift with a 90000 series shock. That spring is 15.83" tall and 660 lb/in rate. All their other springs are 590 lb/in rate.
