Parkers would suggest the 25 has slightly more BHP and faster 0-60. You're right though, the difference is pretty marginal and the 1.4 105 engine is pretty good considering.
Parkers show the 1.4 Rover 25 as 103 ps and the ZR 105 as (unsurprisingly) 105 ps
Not sure where you are looking, performance wise as well as the MG is 9.7sec to 60 and the Rover 25 10.2 seconds /shrug.