Ben..you'll need to experiment as suggested above starting at 1/125 sec..I go to 1/160 sec up to 1/200 sec. That's max bear in mind thst's just for prop aircraft,not jets. . See how they turn out. Bear in mind your focal length in relation to the shutter speed with regard to camera shake.should be at least equal, preferably more..ie. 75mm..1/100 sec. min. Some say equal will do. IS plays a roll too and also how good you ate.Some can take sharp shots at quite low shutter speeds, reallly low..1/30 sec but most can't do that. I actually use a tripod when I go to RAF Brize Norton or Fairford.
You say you live near Mildenhall so this forum will be of great use to you and will help you ID planes.
Scroll down to block 5. You'll see locations of airfields over the UK. Scroll down to East Anglia and amongst the names you will see RAF Mildenhall..and Lakenheath,of course
http://www.fightercontrol.co.uk/forum/
It's THE forum for military aircraft.