If you're using a high quality fully synthetic oil and not beating on the car, then 7500 should be okay. However, the only way to really know would be by comparing UOAs. I'd do one at 3750, then another one at 7500. If the condition of the oil turns out substantially worse at 7500 miles then it would be a good idea to either change it more frequently, or to look into using better oil in the first place.
There are a couple of reasons I change out my oil more often than what is deemed "safe" for a commuter car. The main reason is that making nearly three times the amount of power the car came with from the factory, my engine will experience MUCH higher loads than your average car. This, coupled with high revs (8500rpm), and high heat is hell on motor oil. Also, todays motor oils were not designed with ethanol in mind. Ethanol has different solvent properties than gasoline, and running e85 instead of standard gas causes the oil to separate and break down faster than if I were running gas. Furthermore, I enjoy driving.. while some of my miles may be considered normal driving conditions, much of it would be considered extreme conditions. My engine also has different clearences than an OEM engine, which is why my oil pump was upgraded and modified. And lastly, I spent over $12,000 on the engine in my car and I'm not about to lose it because I didn't change my oil often enough.
That's why I change my oil often, and also why I got a larger capacity oil pan. A new engine costs a hell of a lot more than a $20 oil change. To me, keeping the engine in top shape is far more valuable than a couple extra oil changes.
Bottom line, the only way to know if your oil change interval is sufficient would be by doing multiple UOAs.