Personally I think anything more than a flight suit, gloves, boots and a helmet is unnecessary. In flight fire that engulfs the cockpit has got be an extremely rare event, so the main consideration when deciding on whether to wear protective clothing or not in my opinion should be based on how easily and how quickly you can get out of your aircraft when it goes up in flames after it's crashed! Nomex protection isn't going to last forever. Making certain you open your doors or jettison the canopy before an emergency landing is probably more likely to save you than protective clothing; with which you're only realistically looking at reducing the severity of burns with short term exposure.