I think it moves the fulcrum away from Birmingham, but only for a fairly small area - basically the Thames Valley. Oxford is probably the point where it is about the same journey time via OOC as in the previous comments, but it will very probably be cheaper via B Interchange. Reading, Didcot, Newbury, probably Swindon and Westbury and the small stations in that area will be quicker via OOC as well. Bristol and the West Country will probably be quicker via Birmingham, especially as their connection will be via Curzon Street which should have a lot more trains to the North than Interchange. Southampton and other SWR region stations will probably depend on how easy it is to get to OOC. If there is a way to fit in a couple of direct train to Basingstoke per hour then it'll probably be quicker via OOC. Otherwise, I'd imagine that going via Euston or Birmingham will be the fastest.