AS with most 125's it will depend on the track,
lets take "Lakes", on My RM "T" tight technical sections needed clutching through,(Low first) long up hills with varying grade, you need the gears as close as possible ( I put on 13 /52 )because trying to select another gear at speed up the hill can see you dropping out of the band,I went up a couple on the back sprocket just for that track ,most of the others may be ok with taller gearing
Nepean Dirt track I needed to take up couple off the back (13 /47)
Dissclaimer:
up till this year had 49 on back
I think the front is a 13 but may be a 14
( RM "T" with 520 chain)
going to the 52 teeth on back of 'T" required a small mod to the chain guide at rear