An SP4 would be an improvident purchase for me given the stellar functionality of my SP3 and limited funds. I will buy the type cover, consider the pen and set my sights on the SP5. I don't think I'll go with the Surface Book as I have two stellar premium laptops. I want an ideal road warrior, and the Surface Pro form factor does that best for me. I hardly use the current pen, which I find excellent, so I am on the fence about upgrading to the new one. If I do upgrade, I expect I will not do so immediately. On the other hand, I will get the new type cover the very day that it is available. The current type cover was always more of a compromise than I cared to make.