On my home inspection report, they checked that my house AC temp diff was 14 to 20 deg below ambient just for comparison. So your 20 deg delta sounds pretty good to me. If you look on ackits.com they recommend that you go with a bigger condenser for retrofits. You could also check that your condenser is clean so that you get more efficient heat exchange, and also I have always been under the assumption that flipping the switch over to recirculating would produce the coolest air since you were cooling the same air over and over.

83 4x4, 3" Lift, 33" Buckshot Mudders