Seconded on ear plugs for extended motorway/dual carriageway bashes; they're worth about 10 mph. As far as covering miles goes, I find that quite frequent stops (fag-break length every hour or so, actual smoking optional and not recommended), make quite a difference to the length of time I can sit on the bike for. Stop and look at stuff and don't obsess about distance, though - you'll get somewhere. And get off the motorways for a bit on the way up and down where there are reasonable alternative routes, as you're doing it for fun (e.g. if you are hacking up the M1>A1, consider talking the A68 north from Darlington over Carter Bar, or if you're going up the top of the M6 you can use the old A6 from north of Preston. It's a bit slower and you'll get stuck behind the odd tractor and maybe have to do a little bit of map reading, but so be it. And if a side road looks fun or you spot something interesting to stop and see, go (back if necessary) and have a look rather than thinking "next time", because next time might be a while and you might have other things to do then.
Also, Avon Skin So Soft (available from every small shop in the Highlands) repels the midges (so yes, you'll need something to clean your visor with too...) and keep a small towel in your tank bag for the wet times, as it's a bank holiday weekend. If you're in the far north-west, keep your tank full on a Sunday when you get a chance because places may well be shut or only have very limited hours (I had no trouble going round the top on a CBR6 with a 130 mile tank range and no gauge, though).