Depends on a variety of factors, such as rig (standard, radial, 4.7), crew weight, crew skill, conditions (wind, waves etc.) Generally a Sabre would be slightly slower than a Radial, a bit quicker than a 4.7 and a fair bit slower than a full rig.
Speed is only part of the equation though. Sabres are a lot lighter so feel quite fast, they have good fleets and good racing, and they are an awful lot more comfortable to sail than a Laser 
The question you should really be asking is which is more fun, but we might be a bit biased on that one 