Christmas sales shopping in London help please?

I'm thinking of taking my girlfriend into London for the Christmas sales.. But I need some help narrowing down where I'm thinking of taking her and when is best to go.

Westfield Stratford (I've been told there's a crazy mall here)
Winter wonderland Hyde Park (which sounds 'girlfriendy' haha, plus I think there's ice skating)
Southbank Christmas Market
And Oxford street, but I expect this to be packed!

I need to pick fairly soon as I need to book train tickets as we live just over an hour out from London by train (have vouchers from work, so that expense is covered ;) ). I know she'd love this as she can't afford to splash out shopping for being at uni, she LOVES London (and I know she hasn't been ice skating and really wants to so that might be cool).

My questions are where have you guys heard the best places are to go? Just from ear or experience, and also when are the best times to go? I mean, they start Boxing Day, 26th, but I don't think we'd have as much fun if londons absolutely RAMMED, but then I don't want to leave it so long the best deals die out and all the good things sell out.

Any input appreciated, thank you :)

I see you posted this a few weeks back, but I think by now you should be safe to go without it being too packed. Oxford Street is awesome, but I prefer Covent Garden for shopping! There's a couple of nice little independent shops round there and quirky antique-type jewellery shops but obviously depends what you guys are in to. The other option is to go to the Westfield shopping centre because it has just about everything you could really need! BUT... after saying that, I find it much easier to shop online so you could probably save yourself the trip! I'm into my vintage jewellery, classic watches etc and find it much easier just to deal online!