I just wrote up a post on Blueprint for Financial Prosperity about the differing performance returns of index funds, specifically a Vanguard and a Fidelity S&P index fund, that may be of interest to folks who invest in index funds as a component of their retirement investing strategy. The jist of it was that not all index funds are the same because their reaction times to index changes are different but that that knowledge is, unfortunately, useless because you can’t make any decisions based on it.
Given a choice though, I’d go with the fund with the lower fees every single time.