IMO, since you're considering the jump to FF (don't dither, do it - you won't regret it once the shock of the initial expenditure has passed!), there is absolutely no point at all in buying a Dx only lens. Since I was still a 35mm user until I bought my D700, I have made sure that all my lenses have been FF (or, at least 35mm film) compatible, so had only the expense of purchasing the kit with none of the extra to upgrade lenses to FF. I even parted with my dearly beloved 18-70, the kit lens that came with my D70, when I sold my D200 to my brother in law.