An owner driver twin Honda GX 160 engined kart will do over 80mph on some tracks at full pelt. Rental twins sometimes use larger engines GX180s or even GX220s, however they are geared extremely long to ensure the engines are under stressed.
The top speed therefor is usually down to the individual track and exactly what gears they are running, typically in the region of 50mph (80kmh).
The handling is much bette than single engined karts because the weight distribution is even and the driver sits straight, as opposed to a slight angle on the single engined karts. They have a wider wheelbase and are much more stable and so capable of cornering much quicker than a single engined kart.
This is offset by racing outdoors, with bigger tracks, with wider road and less sever hairpins than an indoor track the overall comfort of driving in the bigger an larger karts is better. You get less bruised in a twin tacit outdoors.