ok thanks for the helpful response. i am looking to up my miles, though still want to stay relatively sharp on the speed front. usually just do 9miles or so on a tuesday, intervals on a thursday (e.g. 10x800m reps with 90secs rest), 11-12miles miles saturday (did 13 today though) and then a gentle 4-5 miler on sundays. used to do lots of speed work (particularly track work) but now beginning to prefer the endurance side of things so may start upping to 15miles or so. did 13 today without any issues and felt absolutely fine. legs not even tired.
generally, my long run routes are very hilly, so pace is quite slow so i'm out for over 90mins (though not by much), personally i do feel better if i take some form of energy drink, than just water. but either way, i'll only use psp for the long stuff and see how it goes.
thanks.