1. Hoist Speed
The difference in hoist speed is quite significant. A crane used for high rise should have a hoist speed of no less than 1m per second and many go much faster, over 3m per second. While a crane used for low rise, a slower winch speed is an acceptable trade off for using a cheaper crane, the delays of a slow winch speed would be too costly on a high rise job.
2. Larger Mast
High rise cranes use a larger mast, this provides more stability and less deflection, especially at greater heights. Most of the 5t cranes used for low-rise have a max tower height of 50m, in part due to their smaller mast, just one of the reasons making them ineligible to be high rise cranes.
3. Climbing and tied in
Low/medium rise cranes are usually free standing, that is, they are not tied into the building. High rise cranes are very often fitted with a climbing frame. At intervals specified by the engineer the tower crane will be attached "tied in" to the building. Beams are attached to the crane tower and bolted to floors in the building
The combination of a larger crane mast and hoist motors leads to larger lifting capacity in high rise cranes
5. Bigger concrete pad
As there is a larger crane mast and more tower crane sections to support, as well as usually a bigger crane the concrete pad the tower crane will be fixed to are much bigger, requiring more concrete, more reo and more room
6. More expensive
High rise cranes are more expensive than the smaller cranes for obvious reasons. They are built stronger, require more tower sections and hoist rope, a larger base to sit on and require a rigging team each time they need to be raised. A builder needs to take into account that costs increase the higher a building goes.
Also keep in mind a crane used for high rise may be used on low rise, generally this happens when there is heavy lifting required such as building out of concrete panels. A low rise should not be used for high rise construction.