Yorkshire Dales 300 would be fine over three days.
The PBW is a bit meh IMO. The section from Gisburn to Long Preston is very poor – I don’t think it gets used much either by bikers or horse riders as it was very overgrown when we last rode it. The Dales part from LP northwards is fine but it’s a day’s ride at most really.
There’s a new ITT route based around Kielder Forest which has suitably located bothies and pubs! 60Km to first bothy, 100Km to second, 40Km back to car lets you do an afternoon, a full day and a morning. Mostly fireroad but the section along the border can be boggy – you also need to check that the Otterburn ranges are open.
There’s two Cairngorms Loops: the original one which goes right round the outside of the range and the ITT which has an inner and outer loop. The latter has some definite hike a bike though!