Those are two wonderful choices you have shortlisted. Both the Lamy 2000 and the Pelikan M600 are great pens. While I do not intend to discourage you, the nib material itself (gold vs. steel) is hardly noticeable, however the nib size, the grind and other factors are most definitely noticeable while writing. Both these pens will not disappoint you as daily writers and as some members have previously recommended, it'd be prudent to top up the pens everyday so that you are always at optimum ink capacity for your usage. I'd personally pick the Pelikan M600 over the Lamy 2000 if money was not an issue. I've felt better feedback from the Pelikan nibs, but it's all a matter of personal preference. Do keep in mind that the Pelikan is significantly more expensive (Rs. 7,000), so do not make the plunge unless the whole package and looks of the pen appeal to you. Having said that, you can not go wrong with either of these two pens.
Coming to the inks, the Diamine Oxford Blue is a great ink with lot of shading, and on certain types of ink resistant paper, you can even see a little bit of magenta / red sheen. The initial few lines of writing everyday / after a break tend to appear much darker and saturated, but once the ink starts to flow, it's a consistent blue with some shading. All the diamine inks I have used behave well in pens and are priced decently.
Hope this has helped, goodluck for your examinations!