If the 6k version had been available when I bought mine, I would have bought it. It likely would have been better for me for a few reasons (a tad lighter weight, etc...). It hadn't been released yet though and the 10k version works fine, so I've seen no need to replace it.
I do think one should buy the one that fits, and not over-size things without having a good reason. In this case though, it's not unsafe and if it's adjusted correctly won't harm the frame, it's just inefficient. Obviously, one would not need as much angle on heavier bars in order to get the same weight distribution.