I just literally switch to Dot 5 from Dot 3 fluid, I really don't notice much of a difference at all if any. The big thing as mentioned above is flush that entire system well. I first drained it and then I vacuum sucked Isopropyl Alcohol through all the lines at the bleeder screws several times, and opened up the calipers and cleaned them thoroughly as well. I also blew compressed air through the open lines to remove as much of the alcohol as possible before letting it dry. Then I disconnected every line and fitting and left them and the master cylinder open for 24 hours to thoroughly dry out. Next added dot 5 fluid and bled the brakes as normal. Oh and don't forget to bench bleed the master cylinder as well, this really help with air bubbles and getting the system pumping well from the beginning, because you want zero air bubbles coming through your lines, most people that I've heard that have complained about a soft pedal later have come back and realized they didn't bench bleed there master cylinder as part of this process and had some air bubbles in lines that they didn't realize was there.
Anyway, as I mentioned, mine feel great and really firm on my fully stock setup, didn't notice any difference really.
Jason