Some generic answers above.. pero kung gusto mo ng mas technical ng konti, eto siguro:
GB is just that, memory na allocated for graphics processing, the more the merrier pa rin, lalo na kung gusto mo masubukan yung Ultra settings
bit = allocation space ng addressing for passing data = (higher number == wider instruction space == more instructions) = faster processes
yung mga "special" features, nilagyan lang nila ng pangalan yung dedicated pipelines for processes i.e. 2 pipes for pixel shading, no-context-switch processing, etc.