Four-wheel drive operates differently. Traditionally, when activated (usually by a lever or button), four-wheel-drive systems lock the front and rear axles together so they turn at the same speed. Some four-wheel-drive systems can also lock the left and right wheels together (using locking differentials) so that all wheels turn at the same
To answer your question, No, there is no speed limit in Snow mode. You can drive as fast as you like. Snow mode will start you in 2nd gear from a stop, to minimize slipping to the wheels, as well as balance the power output between the 4 wheels better.
.