It is a bit hard to say honestly but in looking at caster and roll steer as two different things I see it like this;
With roll understeer
Like I said in a hard turn holding the wheel in a set position and a massive mount of body roll the vehicle/car wants to have the front end steer out of the turn thus making you have to turn the wheel more (sharper) to keep the same rate of turn. I think you can see how this would create stability because the vehicle always wants to "stay under itself/stay going straight"
Lack of Caster causes a wandering issue; While driving the old suspension setup we always had to turn the wheel and literally drive the vehicle. For instance on pavement with heavy truck ruts going straight the car always just drove kind of where ever it wanted and you had to steer to keep it in one lane. Basically there was no self center because of the lack of caster.
The poor handling was a chicken and an egg thing, once it started to wander around you had to counter steer that, (caster issue) which in turn resulted in some amount of body roll, which increased by some amount the steering input (roll oversteer issue) which typically led to over steering the original wander and now having to correct that correction. Do that for 20 or so miles and life sucks. I can count the times on one hand that I could drive that setup with one hand and not look like a drunk in the eight years it was like that, and I probably had several hundred highway miles in that time.
So it seems within reason that roll steer or more to the point roll understeer is important to have, for cornering stability, and caster is important for wandering.
To what degree one can shadow or mask the other I don't know, I have to think that with good caster you can mask a lot if issues, one being roll oversteer as the wandering feeling isn't there so some of the needed input goes away. I know Stephens blazer thing has way better caster and similar roll oversteer to what the car had with the old setup and he has taken it on the UA several times, he also doesn't talk much while driving it on the highway. That tells me that while it's better it's not great.
I have to wonder too if a radius arm setup helps to mask some issues being that the axle is in effect a giant swaybar. There is naturally some compliance in the bushings used etc. but the axle ends up being a swaybar at some point.
but really it's a good way to get the point across that when doing your first link suspension on the front you will be going in circles and dealing with a bunch of bs and feel like you aren't getting anywhere.
that would get me to 5.5" with only a small notch required in the underside of the PS frame rail. My engine is only at 0.5* of rake currently so I could afford to angle it a bit more. 
