As requested (and sorry for the delay), here's the write-up of what I actually got up to that day. I didn't end up having the whole day in the end; I started mid-afternoon. I used Oyster PAYG, touching in/out as appropriate.
Headcodes [in brackets] denote that I've looked up the headcode after the fact so while it's probably the same as it was on 28/3 it may not be.
Code:
1536 1601 2F68 321303 + 322483 London Liverpool St - Shenfield (to Colchester Town)
1605 1629 1K81 321302 + 321315 Shenfield - London Liverpool St (from Southend Victoria) *
1647 1653 [1F36] 720539 + 720537 London Liverpool St - Stratford (to Braintree)
1717 1808 [2O48] 317347 + 317881 Stratford - Hertford East
1825 1843 [2O51] 317881 + 317347 Hertford East - Broxbourne
1905 1934 1O57 Broxbourne - London Liverpool St **
Central Line to Bank
Waterloo and City to Waterloo
2012 2020 2H61 455742 + 455733 London Waterloo - Clapham Junction (to Shepperton)
2021 2028 1H57 377401 + 377450 Clapham Junction to London Victoria (from Littlehampton)
2100 2159 2B34 455843 + 455802 London Victoria to Epsom Downs
2209 2309 2B45 455802 + 455843 Epsom Downs to London Victoria ***
After that I got the bus home!
* This pair later seen at Stratford on 1701 1K72 LST - SOV
** I was the only person on this train!
*** Ran fast from Sutton to Balham due to earlier disruption, arrived Balham 11 early. Had a good chat with Driver Tim while he waited to find out what his calling pattern was!
Thanks to @JonathanH and @High Dyke for helping me fill in the gaps in my notes.
I was not overly impressed with the 720s. Perfectly competent train but the seating follows the "modern" thinking of far too hard and far too upright. SWR's 455s are more comfortable imo, and that's saying something. It was great to get a fast run on a 317; sat in the MSO for some good sounds! Overall it was an enjoyable afternoon/evening out, tho I wish I'd been able to start earlier than I did.
I'm probably going to go out and about either today (21/4) or tomorrow to try and get another fast run on a 317 and some more time on a Southern 455.