If you all remember that video I linked to a while ago, where Gale Banks was discussing boost; he said every 1 PSI you add without increasing intake temperature, you get 7% more power. SOOO 7 PSI with a good intercooler is 49% more power, lets so 50% for easy number crunching. 50% of 300 is 150. So 150 + 300 = 450. Thats a nice bump in power if you ask me
Not to mention only 5 pounds of boost is 35% more power or about another 100 HP, so your looking at around 400 HP with just a little bit of boost, not to mention exhaust mods, intake, tuning, head work etc.