Avnx,
In a nutshell, the big performance difference is in the discharge rate during a start. If you were to plot the discharge rates on a graph the Nicad would be more or less a flat line for a period (3rd start) then rapidly fall off to 0, whereas the lead acid starts a proportional decline the minute the start button is hit. Also if you "abuse" a lead acid it will never recover to its original strength. There are also some extreme temp issues but I have only heard of them. Bottom line is that batteries are cheaper than engines and a fresh NiCad will always win. However, from a support side, lead acid is the way to go as you check them every 600hrs or so and when they fail, they are basically a throw away item, plus you don't need the specialized equipment and training to maintain the NiCad every 60 or 90 days. Hope it helps.
W1