This question is like asking how fast do cars go? Well, how fast does a small car go? Hmmm Define small. Define cost. Define use desired.
A "hobby" small lathe is not very accurate due to lack of rigidity. A small tool room lathe is precise to tenths.
A small "Hobby" lathe isn't powerful and you take several light cuts to get anywhere. A good small lathe will let you take a good bite and get done with the job sooner.
Price doesn't mean a thing sometimes. Tormach sells a "CNC conversion" lathe for silly money but it isn't anything more than a 7 x 12 you can buy from Harbor Freight with an inflated price tag. Same weak motor, same limp noodle rigidity.
A used 10" Southbend that has been cared for will out perform a 10" chinese for rigidity and precision. If this is for a shop and you don't want to buy twice, do NOT buy smaller than 9". 10" is pushing it for a benchtop, but is probably the best bang for the buck when shopping for a bench top sized lathe. Anything smaller and affordable new isn't as precise or robust. There are some great used small tool room lathes available on eBay every once in awhile. Steer clear of the All-in-one headaches.