The fuel system seems to be the most misunderstood portion of a performance car and is usually way overkill, second only to the ignition system.
The power potential of an injector depends on numerous factors. The most important factors you need to worry about are fuel pressure and duty cycle. Most engine gurus will recommend no higher than an 80% duty cycle (the injector is only open 80% of the time under WOT). Fuel pressure will, in essence, bump your potential up by forcing more fuel in. This theory does have its limit, however; eventually the pressure will be so great as to not allow the injector to open.
So, to answer your question: Your average engine will see a max power potential of 385 hp or 307 hp @ 80%. Bumping up the fuel pressure to 50 psi as Killercanary suggested will net you another 40 hp.
Upgrading to 30's will get you nearly 100 hp (480@100%, 384@80%).
Keep in mind that you CAN get too large of an injector. As the injector gets larger the minimum fuel flow gets larger as well which can wreak havoc on your idle characteristics. For instance, if you were to jump up to 42's as someone recommended, your power potential would be in the neighborhood of 672 hp. Expecting 360 hp out of your motor will render these 42# injectors into the 55% duty cycle range. Basically you are only using your injectors half the time. 55% isn't a bad range, though it is far from optimal.
One option you may consider, since the 30#'s are apparently a good deal, is to simply up your fuel pressure once/if you get a blower. 30#'s will satisfy your current needs with no difficulties whatsoever and a small increase in fuel pressure, say 3 - 5 psi, will net you all you need for a blower as well. Top it with an FMU and you're money!
But, if you prefer to leave your system at stock pressure (which is not a bad idea) then I would recommend getting 42#'s if you know you'll upgrade to a blower.
FYI: Injector Sizing Formula
Power = (Number of Inj. * Inj. Flow * Duty Cycle) / BFSC (usually around .5)
384 = (8 * 30 * .8) / .5