Hi Kevin,
Thanks for your reply!
I think my problem with the delete lag might have actually been a seperate issue to the general lag associated with the high DPI retina diplays.
I do experience some general lag typing since upgrading to High Sierra, but this lag with deletions occurred all of a sudden and was much more pronounced.
Anyway, it seems that I have fixed this problem by clearing some caches using the Onyx. Just thought i'd mention it in case anyone else comes across this thread!
Cheers,
Mike