First of all I'd like to thank you for your novice program. It's given me great gains.
Second, I'm up to 335x5 on deadlifts but I haven't put on a belt yet. My work sets don't feel particularly difficult, especially when I warm up properly and apply the valsalva maneuver, but I do usually feel soreness in my lower back for about a few hours after the session.
Many people, especially my friends and people at bb.com, say to put on a belt, but isn't it better for my strength to deadlift without one?