The two (higher OG and higher temp) could be related. Temps are raised to 168-170 for sparge so that the enzymes dilute and stop converting sugars and so the sugars in the grain will be less viscous and flow easier. It sounds like your temps started lower and crept up (I assume you are using a direct fired mash tun instead of a cooler). This means that while it was in the lower range the enzymes did their thing, but as it crept up they diluted and the sugars you had made flowed better so you got better extraction. Was the temperature in the upper 140's to mid 150's for most of the time and then crept up near the end? If so you probably have an acceptable batch and just did an accidental premature mash out. If it went that high almost from the get go you should have very little actual sugar and more of a starchy gruel. If the temperature increase was between these two extremes (i.e. slower) you likely have a very unfermentable wort that will produce a very sweet beer.
Try a forced fermentation. I assume you already aerated and pitched. If you have the ability to hold something at a temperature for a couple days (I have a cheap foam cooler with an adjustable lightbulb and thermometer that I use for proofing sourdough bread), take a sample large enough for your hydrometer to read and raise it slowly to 80 Deg F. Hold it there until fermentation gets done, which will be very quick in comparison to the rest. You will then know what to expect from the batch. That sample will taste awful, so don't bother tasting it--at least not to find out what the main batch will taste like.
