Hi all - thanks to everyone for comments and help. I have now upgraded my MB1 to i7-6700T, 500 GB Samsung ssd, and 16 GB memory. The PassMark rating that I get depends on the exact configuration as shown by the examples below, so we should use these numbers as guides only.
Nothing running except Intel Graphics Settings in the background.
Windows update service completely stopped. (I use WUMT for this and run updates at my convenience manually.)
MB1 using its internal display only: PassMark 9 result is 4028.
MB1 using an external display only: PassMark 9 result is 3937
MB1 using both the iinternal and an external display (extended desktop): PassMark 9 result is 3861
For reference, my original MB1 showed a PassMark of 2429, so definitely worth the upgrade however you look at it! - best regards - Peter