Thanks for the advice everyone - I still can't make up my mind. 4GB DDR2 sticks that fit my laptop look to be pretty scarce already in the UK , eBay prices are higher than buying direct from Crucial and I couldn't find any other reliable brands. I have no use for 8 gigs at the moment but it looks like I will have to buy a new machine in about 4 years if I don't upgrade now. On the bright side if the cpu burns out or something I should be able to resell them.

I thought assigning a flash stick for virtual ram might be a sensible solution but I asked in vain on General help for advice on how to do this with ubuntu 12.04.