Comparing mutual fund performances is a tricky subject at best, and comparing apples to apples is important. But in all such comparisons, management of the mutual fund is to be given a heavy weighting. And it is in this light that load funds should be compared with no-load funds. If you are being asked to pay an extra 3-5% in fees during purchase or sale of the fund, you must be ask yourself - "For whom am I paying this extra fees?" . For example, if you are paying an extra fee for getting Bill Gross to be your bond fund manager, you will probably more than make up your fee over the next few years. On the other hand, betting on management of unproven abilities is a greater gamble - and should not command a premium.
The second factor in choosing load vs. no-load funds is the length of time of your investment. A long-term investment will allow your fees for a load fund to be spread over time, and essentially make it a very small part of your overall portfolio. The cost is real, but its effect can be tempered over time - especially if you get a top notch manager for the premium.
In other words, with a large portfolio under your management, it is best to look for the best management and best long term results for your money, irrespective of whether you invest in load or no-load fund.