Hi Bryan,
On the subject of caster, I do have another question...
I've heard that changing the amount of caster has an impact on the 'feel' of the steering.
More caster increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less caster decrease this feel.
More scrub radius increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less scrub radius decrease this feel.
Since reducing scrub radius is good for turning ability ... but takes away the feel ... and adding caster also helps the turning ability ... and returns the feel ... these are two good tuning changes to do together. . 
I've also heard that caster is often used in a street alignment to offset the irregularities that we may experience when driving down the road.
What your referring to is factory passenger car settings to help the car drive straight on roads that are crowned. Some mechanics like to put a little more caster in the RF wheel to offset this ... others prefer to add a little static camber in the RF to achieve this.
I'm a race car designer & crew chief, focused on track cars, so we don't do this on road course or AutoX cars ... just oval track cars.
Can you touch on either or both of those, particular how either would relate to the KPI / SAI as you explained them above? Is there a crossover point, for example, on how increasing / decreasing the caster will affect the steering 'feel'? I ask partly because if that's true, I wonder if you can hit a point where we might 'overwork' the steering rack we are using? In other words, I would guess that if we make a change to the caster that causes us to have to use more force to turn the wheels, are we possibly putting more pressure on the rack, and risk damaging it?
That question reminds me of a guy one time buying a large duration, high lift, "mean" aggressive inverted flank ramp roller cam to build optimum power in his 434" SBC ... and then asking how the fuel mileage would be? 
Yes, almost anything you do to make your front end grip more & turn better, is going to put more load on the steering box. Wider tires, grippier tires, wheels with the width wider than the tread width, low profile tires, faster steering ratios, more caster, more camber, bigger sway bars, springs & shocks to provide grip, etc, etc, etc.
About the only thing that will help the car turn better & not increase the load on the steering box is reducing scrub radius.
I'm thinking out loud with that question, so perhaps it's irrelevant... But in my case, since I'm using a Ford rack that was likely never built to take much abuse, I wonder if that can become a problem?[/QUOTE]
That's smart thinking. If you build a mean handling machine & utilize a small, moderate duty steering box, you could have issues.
What R&P do you have ?
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