Charles, naturally I'm talking about FSAE cars. Two things stand out for me that I believe make the case of your kart different to an FSAE car:

1. You say your kart steering wheel is around 375mm = 15". IIRC our FSAE steering wheel was close to 8" diamater, I assume most other FSAE cars are similar to this. Again, ignore steering effort, but consider the 'response' of the vehicle to be it's Ay as an output caused by steer displacement as an input. Except this time consider tangential displacement of the steering wheel rim at the driver's hands, or driver arm displacement, rather than angular displacement of the HW / column. For any given vehicle, if you fitted it with A) the FSAE hand wheel, then B) the kart hand wheel, I believe the effective response of case A could be considered as double that of case B.

So, perhaps your kart does have favourable 'response' levels with a pitman arm and less than 90 degrees total lock. But if you tried to achieve this with an FSAE hand wheel of half the size, the vehicle may be deemed too responsive by any normal human pilot.

2. In my experience, karts (vs FSAE) do not have to accommodate such a range of vehicle speeds / corner radii (and hence range of steer angles). This is an issue for FSAE cars as per my previous reasoning - you have a limited amount of HWA you can utilise with a pitman arm, the max of which has to deliver quite a large amount of steer angle for a slow hairpin, meaning your steering response for the high speed corners is perhaps too high. The equivalent high-speed corners for a kart may be long sweepers and may be more forgiving than short duration FSAE slaloms / gates for a driver trying to modulate his steering system which is highly sensitive? I do not know if this is true for your kart / race series, perhaps your range of speeds are more equivalent to FSAE events than I realise. I wonder if you have any Ay vs Steer data to give insight into this aspect?

Kevin, that system sounds very interesting. I'd love to see some pictures / CAD if you happen to have any you'd be willing to share?