In reply to James Raitt:
The Lakeland 3000ers is a long day. You can make it a bit harder, and thus I guess more equivalent to the Welsh 3000s, by adding extra summits: The Dodds are logical, as are Great/Green Gable and some of the Newlands peaks. That puts it somewhere between the standard 3000ers and a BGR in terms of challenge. Here's an article about it:
https://www.ukhillwalking.com/articles/destinations/lakeland_3000-ers_plus_...
and the accompanying Route Card:
https://www.ukhillwalking.com/logbook/r/?i=483
When it comes to big logical hill rounds, Scotland is your oyster of course.
We've got an ongoing article series on UKH that covers this sort of thing. The Big Routes...
South Cluanie Ridge https://www.ukhillwalking.com/articles/destinations/the_big_routes_south_cl... (which you could extend out over Sgurr na Sgine and The Saddle for full effect)
Mullardoch round https://www.ukhillwalking.com/articles/destinations/the_big_routes_the_mull...
All the Kintail Munros https://www.ukhillwalking.com/articles/destinations/the_big_routes_all_the_...
You could do half a Ramsay (all the Mamores, or Grey Corries to The Ben). As per Lochaber Traverse https://www.ukhillwalking.com/articles/destinations/the_big_routes_lochaber...
A few other ideas: Circuit of Glen Coe (like a Skyline, but possibly plus a bit if you like); Cairngorms 4000-ers; Trotternish Ridge; all the Crianlarich Munros...
There's a book (of mine, ahem) full of this sort of thing:
Great Mountain Days in Scotland https://www.cicerone.co.uk/great-mountain-days-in-scotland