Smoothest, fastest,...under 4 pounds....

A recurve sounds like it would fit the bill but thenI would just be a smart aleck...

Certainly High Country makes very light quick bows...Their Sidewinder Carbon is suppose to be a mere 3.1 lb.

Darton Maverick extreme....3.7 lbs

Diamond Triumph 3.6 lbs IBO 308-316...that's smokin.

Parker Hornet 3.8 lbs 310-330 depending on the brace.

The all time light weight is the unique Liberty II...2.3 lbs 300+ IBO but then sling shots don't weigh much...