I have a decent DSL connection (2Mb) and Ive tried numerous brands and card models during the years.
There is no diffinitive winner. I cant say Buy best and strongest curently available and you wont have lag.
Even if you own a super computer and have cards in SLI mode, you will get lag.
WHY?
Because of the L2 engine and its network code. Lets face it, it is an OLD technology to say the least.
Example: If you own a car, lets say some old Ford model 1000cc engine. And if you put a new Ferrari body to replace old Ford one.
You wont go any faster, because in that new Ferrari look you have an old 1000cc engine under the hood.
Its simmilar here but more complicated.
You have a perfect computer on your end, running old L2 engine and on the other end you have this server running old archaic network code.
Whenever a server is full it lags no matter what you have on your end and no matter how powerfull the server machine is.
L2 had lag, has lag and it will have lag in the future.
Sure you can influence it with best gear and top notch internet provider, but these are miniscule changes to the overall speed.
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Some people say they have absolutely no lag in L2 and they get 200+ FPS.
I say, better get a gun and shoot that liar right there and then.
You may have 200+ FPS because you have best nVidia GFX card, but then you still have to face the old network code and have same lag like everyone else at that time. A million FPS wont make any difference here.
Some say "I have no lag in sieges..". I say to them "Dip yourself in acid and stop lying you friggin moron".
All harsh words asside, best you could do Is get a decent GFX card that is capable of playing Unreal engine 2 at 100 FPS and a good Internet provider that has great international connections.