When synthetic oils first came on the market, they claimed that you could extend your oil change intervals. They no longer make that claim. Remember, even though synthetic oil is less likely to degrade at extreme high temperatures, it's going to accumulate particulate matter (i.e. dirt) at the same rate as conventional oil.
A lot of mechanics recommend every 3,000 miles or every 3 months. I am comfortable stretching that to 3,750 and 4 months.
The official recommendation from Honda for the NSX is every 7,500 miles or every 6 months, whichever comes first. You're at 6 months now. It's time to get it changed.