I get so tired of making over sized pieces to have to trim down later. I found the Strip Ruler does the best job for me to make HSTs. You don't have to use this ruler but it takes the math out of it.
http://www.cozyquilt.com/Aspx/Produc...?productID=517
I use my Go dies for most of the HSTs but the dies don't come in all sizes I need.