I'm glad you made this thread. I've been wondering about the 5m grid feature for awhile, and everyone's comments inspired me to give the 5m grid a shot on my new project. I'd like to share my experience working in the 5m grid over the last few days.
Converting from the 10m grid to the 5m grid did not necessarily result in problems. The only baseboard which created a crevice in the ground was the first board. All the other boards on the route I was able to convert without the same problem occuring. I was also not able to recreate that problem, even with new baseboard additions. So not sure whats going on there, but at least its not a universal sort of problem.
Textures did wig out a little bit, it looks like they get pulled into their new respective spaces, which makes them look like rectangles. I was able to paint over the textures though, so I wasn't stuck with the problem some folks have mentioned having. In general, I found that the 5m grid really makes the edges softer (smaller triangles), and it really comes out nice.
The 5m grid effect on the ground itself is also really interesting. Any mountains you build with a cliff face or hard edges will be broken up a little bit, and the results really do look quite natural. I did notice, when I continued to work on the ground in 5m, that it generally takes longer than 10m to build a hillside or a ravine, simply because the elevation tool is working a bit harder. It also seems to take a little while longer to iron out the creases between baseboards, again probably because you're now dealing with a 5m crease instead of a 10m one.
All in all, I think the 5m is a great tool. I didn't have any clippings between a 10m grid and 5m grid in texture or ground, so I think you could use both without too much problem. However, 5m can be cumbersome to move earth around in. Therefore, it might be more efficient to do your gradient work in 10m, then convert the portions you want to 5m before you start to paint.
As stated above, I didn't encounter any particular problem more than once, but watch out! Be cautious, make a copy for sure, and test it first.
