Just one more reason why not to do it:
When I did the exact same thing (MTB triple to Road Double), I had to change the bottom bracket as well (JIS square taper BB), and I also had to change the front derailleur. Most MTB FD's are designed for a biggest ring of 48, and most Road FD's are designed for a 50 smallest ring. I had issues with the MTB FD on a 50 tooth ring, and eventually found a Shimano FD440, which is road curvature, MTB cable pull, and then it all worked beautifully.

And ultimately, it was a largely worthless change, as gear ratio is related to top end speed about as much as shoe size is related to IQ.