Catalyst replacement

[tintin]

I've been told by both Audi Stockport and my local Kwikfit that my cats need replaced - one's collapsed, and one may be about to, so I'm starting to look at options - I've read the thread started by Reffro, which has some useful info, including some specialist suppliers (such as the one use by Jim/Brian in Kirkintilloch).

The cost of OEM replacements is eye watering at c.£1500 each, so I may make an exception to "all OEM" on this occasion, and - as usual - all ideas/suggestions very welcome.

I've got some fairly basic questions to start with tho'

1 - how long can I drive with the car in it's current condition? (it was one of the reasons I didn't make it to last weekend's meet)
2 - what do they do with the old cats? presumably they're worth something, being precious metal n'all…
3 - sports cats seem cheaper and better - why would I not go for those?
4 -should I replace one or both?