Standard gearing on the 250 was 13/47. Front sprocket was chewed out and chain too worn to keep tension. The closest I could get to standard gearing was 14/49 so I did some math before going ahead.
She's a totally new bike! 100Km/h is now ~7300rpm instead of 8000rpm. Overtaking is no different, drop back to 4th or 3rd for extra zip. Around the city streets the lower gearing is better also. No decrease in acceleration off the line. I actually think it works better with a little clutch slip, can hold longer until second.
So if you need to do yours, don't worry about 14/49 messing things up. I reckon it is a better ratio overall.