I've talked to too many people who bought b5 only to continue using b4. If you need the treelab and the other additions, go for it. I personally don't think b5 was much of an improvement over b4... everything needing fixing was ignored, while things I have little or no need for were added. Most reports I've seen say b5 is less stable than b4, which is rock solid. I do like the idea of higher res terrains, but that's about it. Note, this is personal opinion only. I'm waiting with crossed fingers for b6.