My suggestion would be to wait, ane here's why.
Trijicon is completely changing all of their acogs, they are adding new colors, new reticles, and new BDCs.
http://www.trijicon.com/pdfs/ACOG_Specs.pdf
Just me but I wouldn't spend 1k on an optic to only find out damn I could've got a 4x instead of a 3.5x with the same reticle or damn I could've had a green reticle instead of red etc.
As for 3x 3.5x or 4x I really like the 4x. The FOV is what to me was the biggest factor. I looked through a 4x at 100 yards and then a 3.5 and a 3.
Keep in mind that a 3x acog has either a 25.5 ft FOV or a 19.3 ft FOV @ 100 yards. The 4x is 36.8 ft @ 100 yards. It's a big difference to me. The other factor is eye relief. I shoot NTCH and the eye relief wasn't an issue for me on the 4X. Not sure how you like to shoot but for me I can't really see a huge advantage to having more eye relief on something. Last thing is it's a huge purchase unless you're just banking out of control, check it out first hand see what reticle "pops" to your eye after that just pull the trigger you'll be happy you did.