How tough was it when it went in? Since it's a rocket and not a floor, I'd say empty it right out, unless you're really short on time right now, but I'd still do it sooner than later. Then shuffle it back to the 5000 if you need the extra room in the 6500 to finish combining what you have left.
Also you could use a heat lamp to warm the sample to within the temp range. Or you could extrapolate, so what ever the difference is between 20C and 10C, should be roughly the difference between 10C and 0C. I'm not sure how accurate testers are outside of the chart range though.