[Technick]

Just my opinion, I like the 67-68 fastbacks myself. The major difference between the 66 and 67 is the size of the car. The 67 is a physcially bigger car. Not by a huge amount, but defently bigger. 1st example, 1967 the big block 390 is introduced into the Mustang lineup. NO way you stick a 390 into the stock engine compartment of a 66. just can not happen. So that means the 67-68 has more room to work on the engine if you are sticking to the smallblock equation. The 67-68 is a heavier car because it is bigger, bit only by 150-200 lbs if both have small blocks. I personally like the instrumentation of the 67-68. The 65-66 had Falcon instrumentation, which if you like the Falcon is no big deal, but it was the 67 that gave the Mustang the dash and instruments that are "classic" Mustang. Again my opinion. Also you can fit a bigger tire under the fenderwells of the 67-68 than will fit in the 66.
I could go on and on but you get the idea. I am obviously biased to the 67.
One of my best friends has a 66 fastback that we drag race and is a beuitiful car and I would not have it any other way. ( Look at RFedd's posts scattered about these pages. I built the engine ect for that car)