Sadly the i7's from the 3rd generation of intel processors (ivy bridge) cannot support intel graphics, and as such you must have a dedicated graphics chip in your laptop, meaning you can't just go cheap and buy the voyager with intel GMA and save £60
You can later upgrade however you would have the 2 X 4GB sticks left over lying around, so you would have to sell them or just leave them collecting dust
If you choose to go with the optimus, the voyager can only support up to 8GB of RAM though if I remember correctly,
If you go for the 1 x 8gb then you can simply buy another 8GB stick and put that in the future, this costs more money in the short term, however it will save you the hassle of dealing with the left over RAM. (you must make sure the RAM is the same speed (I.E 1600MHz) and technology (DDR3).
As far as I am aware, there is no real difference in the screens in the optimus and the voyager, however there may be some small technical differences, while I do not believe there will be, you might want to email PCS before purchasing just to make sure.
Sadly the i7's from the 3rd generation of intel processors (ivy bridge) cannot support intel graphics, and as such you must have a dedicated graphics chip in your laptop, meaning you can't just go cheap and buy the voyager with intel GMA and save £60
Unless you are running benchmarks it would be difficult to tell the difference in day to day applications. I think that the kingston SSD offers 3 years warranty and the intel 520 5 years. I'd go with the cheapest one.
You should be able to load applications quicker from an SSD, if you selected the SSD as the main drive then PCS will install the OS there.
In most cases you will have the choice to select where to place new programmes. In my case I use my SSD for work related programmes, the OS and main drivers. I use my secondary drive to install games or other programmes I use less often.