I think the larger question for you has more to do with the frequency of your training runs than you fast you can run any individual event. If you're an every other day, or even an every third day runner, then I would advise against an all out 10K attempt as you're body will most likely not be able to recover fast enough to do the 5K at any kind of a reasonable pace.
On the other hand, if you run pretty much every day, then your body is used to the rigors of a higher frequency, and should recover well enough to put in a reasonable effort even after an all out run earlier in the day.