There won't be much real world difference between those 2 CPUs - you can compare them at click here (do a Ctrl+F in your browser, enter 560M / 740QM to go to them quickly).
Regarding the RAM, very few programs will be able to use more than 4Gb RAM, but if you go for more than 4Gb anyway, make sure to get a 64-bit OS. No, I don't think £130 is worth it for only 2Gb extra. 6Gb itself will be overkill for your needs.
Graphics cards (GPUs) come in various flavours & they can arguably make the most difference in a laptop's price tag. FM will probably run well on a basic dedicated one as you know, but other more graphically-intensive games will need better to much better ones. click here gives a useful benchmark comparison list between various GPUs with respect to some games. The GPUs towards the top are the best, with descending performance levels as you go down the list. With a budget of £1300, you should easily be able to get one in the 1st tier, up to a HD 4870. Downsides to a better GPU are lower battery times & increased heat build-up. But I guess it's a small price to pay to play games at good-excellent settings. G