I'm not familiar with game specialized stuff like the card you reference. You can get a Gigabit network card for < $30. How much throughput you actually get will depend on your system. For a network card it seems kind of steep. A few hundred bucks more and you can buy a PC tower with > 4 GB ram with gigabit networking built in. You may want to ask around on some gaming specialty sites what kind of performance you can get with your system and that card.
All I can tell you is my old PC with 2 GB ram had Fast Ethernet built in. I bought a Gigabit network card for it. Typically I can copy large files from that machine to my new PC with 8 GB ram and built-in gigabit networking at a stead 40 MB/sec. The same big video file in the other direction(sent by the newer faster PC) initially shows > 100 MB/sec then tapers off at 60 to 80 MB/sec. What I'm saying is, all other things being equal, the faster machine will be able to send faster. The slow machine can still receive at a good clip.
Before shelling out that kind of cash I'd definitely ask around on gaming sites. Of course if the card is a great card you should be able to put it in a newer PC when you buy one. So it may be an ok investment. But generally buying big hw upgrades for an older PC isn't a great idea unless you built the thing custom with the most advanced components in the first place. PC speeds and capacities advance so fast, that it's often cheaper and more reliable just to buy what you need already together. Unless you enjoy building the units.. nothing wrong with that hobby. But I'd take a wild guess any $30 gigabit card that's not defective would probably at least triple the throughput you get now. Unless you have a super screaming PC it's not likely to be an order of magnitude faster like 10 to 100 Mb/sec was.