Hi again Alf... Ben's advice is good stuff. When I started river fishing for trout and grayling I used an 8ft 6 5wt which served me very well on most medium to large size rivers for dry and nymph fishing. I still think this is a good place to start. As my confidence developed I wanted to broaden my horizons a bit and now I have a range of rods from 6ft 3wts to 10ft 8wt - horses for courses.
Have a scan through the classifieds here there are often some bargains to be found.
As Ben says, reservoir fishing is a different discipline, and the quarry are going to be very different - probably larger fish. So you are going to want something with a bit more oomph. I don't fish still waters so haven't a clue how best to advise you

except that a 7ft 3wt might not be your best option
__________________
"A homeward tramp thro' mist wrapped night,
With heart and creel in common light,
Complete content, the day has brought it,
They fished for pleasure - and they caught it"
P F Morgan
taken from the catch record book at Llanthony Hotel, Honddu Valley, Aug 1942
www.monnowlogue.com
www.monnow.org.uk