I'm a little curious about a point glossed over in this (decent) writeup: what are these situations where one's hourly rate would vary wildly enough to be a major factor? I can see negotiating scope, creating a project price where one might not be as proficient as the resulting price would reward ($100/hr turning into $20/hr), lots of googletime, etc., but since I figure there's no tying these figures to rules of thumb since each situation is different.
Going into it with a fixed rate not left for negotiation unless and until the potential customer asks for it (I've found mentioning it early helps) can greatly simplify one's approach to creating a quote.
"It's all over but the shouting"