White Swan is one of my regulars prior to matches (being going to most games for 25 years and will be at the QF), best on a sunny day as its small inside. Personally I think it’s much better than the Barmy Arms. There’s a short cut round fhe back of station to the ground (Sion Rd, Oak Lane, foot bridge). As above the town centre pubs are rubbish IMO. If not the White Swan I would just get to the Stadium and have a beer in the West Car Park bars, will be really busy of course. As many at the match won’t be Twickenham regulars I suspect they’ll get to the Stadium early so the atmosphere there will be good I think. The West Car Park bars will probably be showing the earlier game.
Post the match the bars around the stadium can have a good atmosphere and allow the crowds for bus / train to subside a bit. There are lots of extra buses laid on for the RWC inc closing the A316. As such a trip into Richmnd could be good, somewhere down on the river again – say the White Cross ? Really just follow the atmosphere ? Twickenham Church St as recommended above, we often get a drink and/or or something to eat
Enjoy the game should be a cracker.