I'm not too bothered about speed increases in the Hope Valley, the main problems are the number of freight paths (esp the cement stuff to Hope), the single chord at Dore and the "all stops" Pacer service (which cannot be overtaken by TPE/ EMT services).
Sort the layout at Dore out, provide some more loops and try to speed up the Pacers - that'd make a bigger difference than increasing the top speed (and being caught behind something in front).
To put things in context for those who don't know the area, the roads from Sheffield to Manchester are the single carriageway A57 (Snake Pass) or the single carriageway A628 (which connects with the A616 at the Flouch, taking you via the accident blackspots of the Stocksbridge by-pass). Either route involves tailbacks around Mottram...
...so, there's not a fast motorway linking the two cities (compared to the M1 from Sheffield to Leeds or the M62 from Leeds to Manchester). So, speed isn't as important for rail to compete on - capacity is (both in terms of the half hourly frequency and the length of the trains). Passing loops (esp at Dore!) and trying to sort out the freight/Pacers would be more beneficial (in my eyes)