Ok, I hadn't tested with both before. Keeping the array alive and using --nouse-osr makes io.js only 2.3% slower than my original measurement for Node 0.10.35. Median of 5058ms.

And Node 0.10.35 shows basically the same results as before. I see less than 1% difference. Maybe just random fluctuation. Even if not. 1% is irrelevant.