The longest stretch of Meter Gauge in running condition id from Kasganj to Gonda in Northern UP. Its 500 kms. An express train takes almost 13 hours to cover this distance. An average of less than 39 km/hr.
I would like to differ from you in preserving the Meter Gauge. This will be very uneconomical and these locos and rakes are not kind of antique. they are very similar to the broad gauge locos and rakes. May be a few isolated stretches can be preserved but if it can be converted then it should be done.