Percent utiilization is a sliding scale, and only FICO knows the exact impact at various %util levels. Anecdotal experience from most on this site is that util above 50% has substantial impact, and that %util below 10% is best.
Your situation is a great example of why having larger CLs is real important. If you charge $300 on a $500 CL card, that will put you above 50% util, while charging the same $300 on a $5000 CL card will put you under 10% util.