If you select a traditional 1.6 GPF gravity San Raphael, it will use Kohler's proprietary flush-valve/flapper assembly. These parts are "standardized" in that they are designed for Kohler's one-piece gravity fixtures. Kohler fixtures, and presumably parts, carry a one year Warranty.
If you select the San Raphael Pressure-Lite, it's a 1.0 GPF HET (High Efficency Toilet) equipped with Flushmate pressure-assist system. Flushmate parts are "standardized" and readily available locally, online, or from the factory. Flushmate provides a ten year Warranty on parts and a lifetime Warranty on the pressure-tank.
As with everything else, it's best to weigh your options and in the end, choose whatever suits your specific needs.
Hope this helps.