Depending on where your timing is set right now, it may just be a little more power, or a substantial amount. I don't know why it happens, but I seem to read a lot of posts where people say that they checked their timing and it was only 6-8° of advance timing when stock is 10°. Considering you can sometimes push it to 14° or more, those people see a huge gain in power (relatively speaking). I didn't notice any huge change, but that's because my timing was already set around 11° when I got the truck from my dad and I only advanced it by 1°. This weekend I'm looking to try pushing the timing a bit further again. It won't be a huge change, but every bit helps.

Generally speaking, as you increase timing, it's going to move the peak torque and horsepower up in the RPM range. If you stay with 87 or 89 octane fuels, you won't be able to advance the timing far enough to really feel any difference in where the power band is situated, but you should notice a bit more power overall. Also, as timing is increased, it will help improve the efficiency of the motor slightly, so you may see a slight increase in fuel economy (but don't bet on it with the 460).