correl i think you are worried over nothing. the original sierra setup doenst come into play here as the only part we are using is the hub.
the reason why we dont use the sierra bottom ball joint is for the reason you are trying to get at. it cant take the forces we want it to.
the maxi ball joint was chosen as it is a lot stronger and designed to be used in a twin wishbone design rather than a Mcphereson setup.
as far as i am aware almost every kit car manufacturer uses the maxi joint and i have never heard of one fail ever, even under racing conditions.
the other thing you need to think about is how many miles do you do in 2 years in your daily driver before the ball joints fail? at a rough guess it would probably take you 10 years to do the same mileage in the roadster, factor in the extra strength and the lower weight and i doubt the ball joint would fail in a very long time.
as for speed bumps you dont need to worry, you will only have about 100-120mm ground clearance so wont be going over any
