Its really interesting to read everybody's opinions on howardo's post. My first thought in response to Rowuk's post is that I can practice for an hour a day (about all the time I can spare) and still play a 4 hour gig on lead in a big band. So I question the need to practice double the performance time. However, maybe the demands of an hour long solo performance are different to lead in a big band where you get to rest intermittently during pieces. I imagine it also depends on how efficient your technique is.