smoother surface... maybe...
Flat surface... not quite...
I have machines that can measure surface flatness quite well here. Out of 4 rings I had in hand... 2 of them were not quite as even as the other 2 were.
As for smoother, here is what you COULD do... (not that I would bother).

1) Sand as mentioned... on flat surface. Suggesting something like at least toolrom grade B. Probably can find decent one around $100 or so.
Finer grade such as 1000 would be better with wet sanding. Just take your sweet time doing it.

2) Time to use metal polisher with proper polish compound. You will get mirror shine on it. Now the only thing is... you might have taken away a little of flatness you worked hard to get on 1).

Lot of extreme computer Overclockers do these day in and day out on their heat sink, etc...

Is it worth it? I think RC is hobby where excessive is norm anyways... (like any hobby is really).

The point of sanding the diff rings is to eliminate the warping caused by the diff rings being stamped out of the raw material. The burnishing left on the surface is similar to a bunch of little hairs all stood up. When you break in the diff it lays the hairs over and creates a smooth, perfectly flat groove. The groove allows for a larger contact area. That allows the diff to be run with less tention and still not slip. This is all info straight from Fred from bfast.

I am privledged to have a service grinder at work. Drop 6 rings in a row, turn on mag, add fluid, graze 1000th, flip, graze 1000th, figure 8 on 600 grit, spray with nitro cleaner. Bam, done. Pretty close to the B-fast process with the service grinder.

we (i, actually) stopped lapping chips and heatsinks a few years ago when manufacturers started putting a concave profile to the chip for more surface area and consistent contact. the really hardcore guys would grind chips until the aluminium was nearly gone and the copper or nickel base was visible

i use a big, thick piece of aquarium glass, 1200 for starters and generous shots of wd-40. proper technique on diff rings is easy - 3 fingertips at 10, 2 and 6 o'clock, figure 8's all over the paper, then turn 1 hour and repeat several times. smooth? yes. flat (which is what i wanted)? probably not.

The 800 grit may be your problem, but not in the way you think. I met Fred (the owner of BFast) at a race and had an in depth conversation about his process. Before starting BFast he was a master machinist. He knows what he is talking about. He told me to start with 800 and really light pressure. If you use too much pressure it will just force the ring back flat, instead of removing material from the high spots. After the 800, 1000, then 2000. My diffs are butter smooth, so smooth they feel fake. I really don't know how to put it other than they feel fake. Almost like there is no diff. They stay that smooth until the grease in the thrust bearing inevitably gets dirt in it; usually about 6 months. This is running a 7.5 in my buggy on a track that regularly runs slicks, and 17.5 no timing buggies can hit wheelies on demand so I'm not banging the diffs

Assembled AE Big Bore shocks tonight with the clear Kyosho X rings(Part number ORG03X), and they sucked air past the X rings as i bled them(before even putting on the caps). The X rings are too big in the center, and the shock shafts are slightly smaller than the V2 shafts. I do not recommend trying them as wasting your money, they felt smooth but did not seal against the shaft very well at all and would suck air past them with any side loading of the shaft. I put on the AE O rings and they bled perfectly, and i could not get them to pull air past the seals no matter how hard i tried. Also i've heard good things about the losi O rings, so i use either brand(losi and AE look identical). Hope this helps someone

what's the possibility that sanding the diff rings by hand could lead to an odd angle on the diff rings? wouldn't that give you an odd feeling diff? the diff balls could be riding lovely on two thirds of the ring and not so on the other third. you could press down evenly on the rings as you sand them, but what's the possibility that you're doing more harm than good?

I use a spare female diff half to hold the ring and apply pressure evenly.

this is what I'm running also

I know this topic as been beat to death. But I didn't see a real clear answer. I'm going to be running on high bite carpet. Do I want the "c" hub with shaved brace. If not, what is the best to free up the rear end. Thanks

The C hub with shaved brace will work and possibly reduce the rear toe.

Im looking for some green fronts too. I ran black fr white rr lastnight. It was ok but grenn in the front would be perfect.

For anyone looking for AE Springs...check out losipartshouse.com, they had quite a few when i got mine a few days ago.

How are the new AE springs? Good quality?

I have heard they are as good as the Kyosho springs. Im hoping so because i like my Kyosho springs on the car but like the $4 price of the AE's.