I am wondering if the D-series gears are interchangeable (particularly 96-00 DX hatch gears) in the sense that 3rd can be used as 4th, and 4th as 5th.

I got to thinking about this once I saw the infinitude 3/5 gears on http://www.mfactoryhk.com. For the EX transmission you use their shorter 3rd gear, stock 3rd as 4th, and their shorter 5th (stock 5th works too). This gives you gearing similar to a 99-00 Si.

Now, I want to use the infinitude 3rd gear and then essentially shift the other gears up. So stock 3rd as 4th, stock 4th as 5th...and get rid of the stock 5th. If this is possible, it would give me gearing that is very close to a hydro GSR (besides 1st & 2nd - they would be longer). I am doubting this idea very strongly but I figured I'd better ask because it would be a cheap way to get better gearing. Tons of unwanted DX trannies out there I'm sure and the infinitude 3rd is only $325.

Here are some graphed comparisons on http://www.fatboyraceworks.com (green is my hybrid one):
Mine vs Stock DX
Mine vs Stock EX
Mine vs Infinitude 3rd EX
Mine vs GSR

As you can see it's fairly decent gearing, especially when compared to the stock DX...which blows. You hit 3rd using stock DX gears and the car falls flat on it's face, and 4th will make you cry. I was also thinking that if I couldn't use 4th as 5th then the stock 5th could stay. It would allow the rpm's to drop big time but I guess that isn't such a big deal. Thanks guys.