In response to Robbo1509 the distance from Victoria to Euxton Jcn is 25 miles 31 chains. A quick attempt at the distance from Victoria via Parkside (four different mileage sequences) gives 31 miles 21 chains. Preston is 5 miles 35 chains beyond Euxton. So the Wigan route is roughly 20% longer than the Bolton route.
It's about the same distance on both routes to get clear of the severe Manchester speed restrictions (though the Bolton line could quite easily be made somewhat faster if there's any major rebuilding of Salford Crescent). The only severe restriction is then the 20 at Bolton itself (which will no doubt have to stay). And we read that this line is to go up to 100, even through Farnworth tunnel.
Via the longer Wigan route you have 90 once you get on to the Liverpool & Manchester line, but down to 75 over Chat Moss (still only 60 in one direction), then three-quarters of a mile at 20 through Parkside Jcn, Lowton Jcn, and Golborne Jcn, then 110 to Wigan, 80 through Wigan, and 110/125 on to Preston.
It's hard to see how the Wigan route could ever begin to match an improved Bolton route for journey-time even if there were to be some major work at Parkside. And why is commuter traffic from Wigan more acceptable than from Bolton? Finally, what about the fact that Wigan gets a generous Scottish service from London and Birmingham trains, whilst Bolton has no alternatives?
It's fairly clear that would be record-setting...
