How up to date are or is this graphic card(s)?
nVIDIA GeForce GT 650M (Optimus) + Intel® HD Graphics 4000.
The 650M is probably decent for a laptop card, but low-end for a desktop card. HD4000 is integrated - by itself, worthless, though I suspect you are looking at 3rd Generation Intel laptop or AIO, in which case it makes n difference since you would have the nVidia card to do the real work.
And also what Nvidia Ge-Force with three numbers on the end as shown, is equivalent to the 8600 or 8800?
Very open to interpretation with the 8800 but I'll assume you mean the 8800GS. There really isn't that much on the market that is that low. Maybe a GT220
And on a site note, would you notice any performance difference between say an i3 & i5? or i5 & i7? (And why do these "i" seem to go up every second number?) The most important question though is about the video card.
As mentioned before, raw, "clock speed" GHz will help the most with Trainz. There is little real difference between the i3, i5 and i7 themselves, aside from the speed (GHz) available out-of-the-box. i5 and i7 will have 4+ core, but that really doesn't help much with Trainz in Driver mode at present. With a decent desktop, you can bump (overclock) the speed of an i3 or i5 to meet or exceed that of a stock i7 (though the i7 can be sped up too) so it becomes somewhat of a wash and the real difference is mostly the number of cores you need - which is only 2 for most Trainz purposes. Some folks might argue that the 4 cores of an i5 (or 4+ of an i7) help with non-Trainz background tasks or the extra crap imposed by some operating systems. Overclocking is not an option with most laptops, All-in-ones, or many OEM desktops.
As for the use of odd numbers in the i-series, I guess that's a marketing thing by Intel.