I agree with fox, on a well, if you want to be really effective as a "sniper", you'll want to work towards swapping out all your internals (Even with the higher quality Maruzen this was the case), and possibly doing modifications to your stock.
The PDI hop-up really is the way to go, you'll have more selection for tightbore and hop-up sleeves you use. Had my gun not had an OK tightbore barrel that worked with the stock hop-up with it when I bought it, I would have gone to the PDI.
For internals, when you can go with lay lax for guaranteed reliability and quality. (in my research I never heard of any problems from using lay lax parts). However, research may point you to some equally good, yet lower cost options out there. Keep in mind the equally good, especially for a 'sniper rifle'. It's a niche that's hard enough in airsoft that you really want the best you can afford. And by afford I mean saving up for a long time and making it a year long project if need be.
Also, start your ghillie suit now, it'll talk a long time to make.
(On this note; I already really miss my APS L96. Darn you financial needs! Darn you!)