My firsthand experience is that if you do a good job on the extract and consume on an empty stomach then the effects come on as fast as anyone could wish (noticeable in 10 minutes, full in 30). I have never used anything but a combination of olive oil and butter. THC is fat soluble, so pretty much any fat should work. Decarboxylating - heating at low temps first - is very important in cooking for maximum benefit. I don't decarb as much as some, but some decarboxylation also occurs in the cooking process.
You are right, the better your preparation the less you will need to use. Nowadays I mostly cook with leaf, which is a little harder to gauge. But I did cook with some bud last week. My wife and I split a gram and that was more than enough.