Out of curiousity, at which speed did you measure the 5mph difference? In my experience, the higher the speed, the greater MPH difference you will see.
I do know that my 2.73 Jeeps both are running 31's, and a 24 tooth gear got me almost dead accurate, so I would think that a 25 would be closer to working with 30x9.50's. I don't recall what the stock gear was on either of my 2.73 equipped Jeeps was (one came stock with 235/75/15 and the other came with 205/75/15 so they were different gears from the factory dependant on OEM tire size). There used to be a gear applet for speedo gears, but it doesn't work anymore.
85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT
85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO