226mile 30ch, i believe is the shortest route, taking the following route,
Route: Plymouth, Lipson Junction, Laira Junction, Tavistock Junction, Hemerdon, Ivybridge, Aish Emergency Crossovers, Totnes, Dainton Tunnel, Newton Abbot, Teignmouth, Dawlish, Dawlish Warren, Starcross, Exeter St Thomas, Exeter St Davids, Cowley Bridge Junction, Stoke Canon Level Crossing, Hele & Bradninch Level Crossing, Tiverton Loop, Tiverton Parkway, Wellington (Somerset) Crossover, Norton Fitzwarren, Taunton, Cogload Junction, Athelney Crossing, Castle Cary, Bruton, East Somerset Junction, Blatchbridge Junction, Clink Road Junction, Fairwood Junction, Heywood Road Junction, Lavington, Woodborough, Pewsey, Savernake, Bedwyn, Hungerford, Kintbury, Newbury, Newbury Racecourse, Thatcham, Midgham, Aldermaston, Theale, Southcote Junction, Reading West, Reading Oxford Road Junction, Reading, Twyford West, Twyford, Ruscombe, Maidenhead West, Maidenhead, Maidenhead East, Taplow, Burnham (Bucks), Farnham Road (Slough) Loop, Slough, Dolphin Junction, Langley (Berks), Iver, West Drayton Junction, West Drayton, West Drayton East, Stockley Bridge Junction, Heathrow Airport Junction, Hayes & Harlington, Southall West Junction, Southall, Southall East Junction, Hanwell Bridge Loop, Hanwell, West Ealing Junction, West Ealing, Ealing Broadway, Acton West, Acton Main Line, Friars Junction, Old Oak Common West, Old Oak Common East, Ladbroke Grove, London Paddington
2hrs 17 would be an average of approx 100mph taking this route,
sourced this info using
http://www.mileage.railmiles.org/