no problem with the DV. I have compared the DV with ones out of a 10mm MW IP. Also I have directly compared the DV with the orifice and without in the same IP with no difference on the bench. Regarding the collar the DVs of the small 5.5 IP are the best in sense of narrow collar.

I tried several after market elements (at that time M) and it seems to me that they are identical origin.
Take a close look at the control edge. This edge has to be without radius. This is the reason why grinding the hardened part is the only way to do it, no EDMing. Edges with visible (shiny) radius are bad quality. No problem, but the detailed geometry is slightly different and will result in different flows at different rpm and positions. You can not balance them well in low AND higher rpm ranges. Some people live with crappy idle (its a race car) and focus on balancing the high rpms.
Before changing the edge I would rather touch the "gearing" of the governor levers to expand the operation range (let's assume you have good quality elements), but I took the decision that this is more complicated than just making new elements.
The precision of manufacturing elements is far beyond what a good machine shop can do. I also asked those guys but the answer was the same for all of them.
Do a search there was a guy who had 8 mm installed but he stopped posting.

Tom