I prefer six, but have gone with 4 with no major issues in the past. Actually, in the past I've power-napped it for like an hour in my car and been relatively okay.
Working 12 hours overnight on the weekends, and doing University during the days will do that to you...
2014 BMW 435i XDrive M-Sport - Delivered May 2014
2007 BMW 323i - Delivered April 2007