I think if you were to quarter the plums they would freeze well enough for cooking.
Pears go well with blackberries in crumble and pie. You could also steep the blackberries in gin and sugar for a good couple of months in a kilner jar for a very adult pudding, or if you use more gin (use a 75cl bottle poured into a 1l bottle and top up with blackberries and a little sugar for a very adult drink!
Thandeka- now you're talking with pear tart! I'll send you one once i've perfected it <don't hold breath!> Good luck w pg!
OhYouBadKitten- dad's home-brew has put me off wine making for life <phew> but I do like the gin idea. I didn't know you can still get kilner jars: we used to have a stash under the spare room wardrobe when I was a kid!