Thanks for the replies, much appreciated -

Right, good to hear - i'm going to promote Scrumptious in place of discovery. They sound similar flavour as well as similar time (I see Discovery and Golden delicious are the parents of Scrumptious) so i probably should only have one. The other issue with discovery might be that its a partial tip bearer(..?) From what i understand that can still be ok for heavy pruning but requires a slightly different approach and might result in a less tidy shape.(..?) And I've probably got enough to get my head around without complicating it further(..!) Thanks for the Topaz tip, considered it, but think my final selection is:
Scrumptious, Red Windsor, Egremont Russet, Herefordshire Russet. (nice symmetry with 2 reds and 2 russets!). Pollination looks good...

M9 sounds about right.
Scrumptious is very good - a few days later than Discovery, slightly better flavour imo.
I'd add to your list a more recent Czech variety - Topaz, very reliable cropping and superb flavour, pick mid Oct, finish eating by early Nov.

Rod