I quickly realized that to catch class 43 or 158 all one has to do is go anywhere near the track and wait - so not much fun. Chasing goods trains seem to be more exciting option (not so much when they do not appear where and when they should).
So once I found this info:
1042 Winchester to Southampton Airport Parkway
Runs WO on 22/05/2013 only
Wantage Road 1334-1356
it didn't take me long to decide to have lunch on the go and capture that mysterious train.
The decision was made easier as earlier I tried locations around Wantage Road anyway (nothing particularly good, but about that soon), and also found these photos :
http://table158photography.weebly.com/uploads/8/2/1/2/8212554/dpp_2925.jpg
http://table158photography.weebly.com/uploads/8/2/1/2/8212554/dpp_2927.jpg
and couldn't quite remember such a view at Denchwort.
Here is the expected train approaching, met by 1B35 London Paddington - Swansea:
When it got closer it appeared it is not a goods train, but some special - 67020 + 12 Pullman coaches + 67028
I have no idea what was that, maybe one day I'll learn how to dig up more information, for today only short timetable showing loop route of that train:
Winchester 1042
Southampton Airport Parkway 1052 1057
Salisbury pass 1151
Chippenham pass 1257
Swindon pass 1316
Didcot Parkway 1406 1408
Oxford Road Jn 1434
Winchester 1538 1543
Southampton Airport Parkway 1553