<< My other plan was to buy a second NVIDIA geforce GTX 550 Ti and SLI t them, coul dpick the card up for a s l;ittle as £50 so may be a cheap upgrade option. >>
Don't SLI two weak GPUs (it'll probably give you 10-15% performance boost), you'd be better off selling the GTX 550ti & get a GTX 760 instead.
<< I have already purchased a SSD but have yet to install it, do u think this will help? >>
Yes indeed, loading time will be much improved.