I have no experience with endurance racing, but I am an experienced herbalist.
Ginseng and caffeine are different.
First(excuse me if this sounds uptight~:) caffeine is a component of various herbal and food products. A better comparison would be caffeine and ginsenosides(components of ginseng) or green tea and ginseng.
This brings me to another point: caffeine comes in various forms including isolated extracts and as a part of natural foods and herbs(coffee beans, green tea leaves, cocoa beans, etc.)Choosing the right form of caffeine for your body type can help acheive optimal results. For example one person may get low blood sugar from plain green tea leading to a 'bonk' but the same person might find sustained energy from a black tea chai with milk and sugar. Coffee might suit some people but not others, etc. Combining caffeine containing products with other foods can help bring balance(think about a fire, it always needs some substance to burn otherwise it goes out.)
Also let us not forget herbs with chemicals in the caffeine 'family' such as yerba mate or guarana.
On to ginseng. Ginseng is not a stimulant specifically rather it is a tonic herb. It has adaptogenic qualities meaning that its effects vary depending on ones bodily needs. It can have seemingly opposite effects on different people. I have taken ginseng and been put to sleep, go figure!!
For some people ginseng can overstimulate, especially younger adults and those with high blood pressure. Younger people may like the herb astragalus better. Siberian ginseng is another performance enhancing herb with less potential adverse side effects than ginseng.
For best results consult an herbalist as PJ suggested. You can always experiment with different things though, just watch out for overstimulation(feeling angry, too hot, irritated or like you might burst.)