here's where this gets weird:
both paragon and racer's edge say the effective rate of the rear springs is low (.56 and .43 or something respectively)
that means that an 800# spring is really only 448 and 344 depending on which number you use
add the torsion rate if you have them (175), and you get in the range of "normal" with a 650 up front - no torsions, and the rear is way too soft
a hatchback starts out 66# heavy in the rear - that means it needs a higher rate spring just to be even to the front
the stock front 160# springs are 94% effective making the wheel rate 150# - the stock rear wheel rate is 175 - that makes a front to rear ratio rear biased - the ratio is .859:1
plug in any rates you want to from there
so, either they are both very wrong in the math, or a lot of people are springing their cars too soft in the rear - you be the judge of which - i only know what i've found out on mine so far
i started with 250 in the front, went up to 400 and back down to 300 with stops in between, and 350 in the rear and went up to 600 and back down to 500 with similar stops in between - this is now balancing fairly well against the 300 up front, given that i am still probably about 75# light in the rear due to the nature of being a cab, and all the weght reduction stuff i did, even after moving the battery to the trunk
if a car "feels" like it's handling right, it may merely be masking setup issues - a lot of people make the mistake of adding a ton of camber to correct for oversteer when in reality it is a spring, weight balance, or sway bar issue - while the rule of thumb is that stiffer springs cause oversteer, a spring that is way too soft can do much the same thing, but in the form of power oversteer
i found a lot of this out the hard way, when i was young and thought i knew everything, disagreeing with my mentor about setup for a long time - then he told me to just shut up and try what he was saying - i did, and he was right - then he walked me through the physics of it and how one thing can mask another, and while you think it's right and it even "feels" right, you are actually scrubbing speed off in a corner - it really showed up in my brakes and tires - after i did what he told me to, i got twice the life out of both, and was a good 2 seconds a lap faster
one of the big problems is that even the M030 swaybars are not nearly big enough to correct the suspension issues - you end up springing the car firm in the front and soft in the rear, and then adding a ton of camber, or really huge tires, just to try to keep it stable and stop sloshing around - i just went through this - i tried at least 7 different sets of springs trying to figure out what the heck was going on, and why the car was not behaving like the books said it should
a quick look at film of a car will tell a lot - a car dipping in the outside rear or lifting the inside front going into a corner says the rear is too soft relative to the front
the solution for me was bigger sway bars - i took it for granted that these M030 bars were the things to use - it turns out that it was only because there was nothing else out there - so, i made bigger ones - now i have nearly textbook spring rates and almost no body roll - the car is definitely quicker in the corners, and a lot more stable - i'm still a touch soft on spring in the rear, but it is a street car after all, and this makes it comfortable - i will finally get a chance to see just how much better it is when i get it out on the track later this summer
it would be interesting to compare lap times over the years of cars with different setups
this is a fun discussion though