Do the VX gears...if you are wanting to improve fuel mileage. I used to get annoyed with people grabbing the 5th gear out of junkyard crx hf cars for their SI or DX cause that was one less spare transmission for me. I'd do around 1800 rpms at 60mph. 3rd, 4th, and 5th were overdrive gears!
As for the HX vtec...from what I've gathered is that the vtec-e doesn't allow the valves to all open all the way until the v-tec is engaged then they open all the valves all the way. At lower rpms you don't need the valves to open all the way if you are looking for economy.
Also, in rebuilding my HX transmission I found a number of sites (no linky at the moment) that showed the HX having lower gearing (numerically) than the other civics. Also, the VX was lower and my crx hf was the lowest of all
