The night before a long run...

Does anyone else set up the night before a long run and debate on how far to go? I have been running 6 to 7 miles, but I want to step up to 8 or 10. I am not sure if I should try for 10 tomorrow or just be happy with 8. I plan on running the half marathon in Oct, so I still have time to build up to it. I think I will just go for 8 and leave the 10 mile run for later. Well, off to bed to get some sleep before tomorrow morning's run. I will post tomorrow on how I did.