There's no hard and fast rule.
It's just like when people tell you it needs to sound good acoustically. It's not always so.
Man, I thought you had it until I realized that it is 7.38560486879493739 lbs. Wow, that was the closest I have seen anyone get to the right answer. I think this thread will again prove that there is no ideal weight. Check my signature at the bottom for a quote from a fellow TGPer that pretty much sums it up!7.385860486879493736 lb
but most of the time it is. at least for the kind of sound i like. the pickups should be good enough to get the acoustic sound of the guitar. a loud guitar unplugged with good pups = yummy.
anyway, for strats, i like them feather light. as light as you can get em.