£50's much preferred if available - far less pfaffing about. Nearly a decade back, just after Lehman and relatively flush, I was worried by the possibility of a currency collapse, so I bought a bunch of high-value foreign notes just in case of a zombie apocalypse (because zombies like big notes, as any fule kno). Mostly they've just sat there, slowly wasting away; but recently I decided to enjoy them with a renaissance of punting, after a longish break - hence the recent spate of reviews.
The prize has to go to the Swiss and their very beautiful (in every sense) notes. They have one for 1000 CHF (something like £750 these days). Unfortunately, they're not yet the go-to currency for Barnet prossies.