Hi,
You'll do well to look at Chrun pool near Cirencester (not summer though as closed from end of July).
I have only fished Salford (near chipping norton) once and absolutley loved it, had my first two fish ever on a dry

, the fish don't seem to be very big but thats not the point for me. it's quite, there are two lakes and the water is gin clear.
Lechlade (bushyleaze) also Gin clear is o'k in summer but fishes better in the winter as in really well. having said that, there a few anglers that never seem to fail to catch anytime of year. The other lake (Lechlade lake) is where the really big browns and Rainbows are to be found, I think Browniebasher on here would a good fellow to ask about that.
Watermark up the road from Churn pool in South Cerney is also good but not my cup of tea (I wasn't built for floating casting platforms)

they also have a stretch of river (churn I think but could be the colne)
The river Colne in Fairford, controlled by the Bull hotel adjacent the river is also supposed to be ok but I've been told that the public footpath alongside also means noisey people and dogs jumping in the river
Brook Farm is one of the nearest to you in Cheltenham but is syndicate only but the fishing sounds superb for big stillwater trout.
As posted above, there is also a small syndicate on the Churn outside Cirencester (Cheltenham side so quite handy), it is very much small stream type fishing but also very quite and absolutley private, part of it runs through a private estate, they also have a lake of humble proportions that is fishable from a small punt.
I hope this helps,
Chris