^You're not calculating journey times based on those worthless warp speed charts from the technical manuals, are you? They've never had anything to do with the warp speeds in the show, which have always been totally random, from TOS through to STXI and everything in between.
I knew somebody would fall in to this trap. It doesn't matter whether the warp speeds can be quantified or not, the issue is that Warp 9 is comparatively much faster than Warp 4. If it takes Enterprise ten minutes to reach Earth at Warp 4, a ship from further away can get there much faster at Warp 9. Or is Warp 9 slower than Warp 4 when speed of plot is applied? It still isn't clear how Enterprise beat Narada to Earth, so maybe...