I am not familiar with the sizes. What would be equivilant to size 11 mens boots and what is the best length of ski for a 5 foot 11 inch man?

A size 44.5 boot is equivalent to a US size 11. As for best length of ski, nordic skis are actually fitted by weight (longer lengths are generally also stiffer, meaning that the ski requires more weight to compress the grip area into the ground). This is important because too stiff of a ski won't provide enough grip (no contact of the grip area = no propulsion because the rest of the ski is simply designed to glide) and an overly flexible ski will have the grip area constantly in contact with the snow, slowing you down in a similar manner to having the emergency brake constantly engaged in your car.