Considering your specifications, there's obviously something odd going on in your case. I just have a few things to note real quick before getting into the meat of things, as honestly they won't affect your problem.
1: Mario Party 5 is kinda hard to run because the INI defaults EFB2Ram on.
2: Kirby Air Ride works in Dualcore, I haven't been able to desync. It's literally the second easiest game to run on netplay behind Mario Party 4; which also works on Dualcore.
With that out of the way, have you tried older builds? Netplay has gotten wrecked by half finished features and such as of recent. I'd heavily recommend trying something like 3.5-1789.
Are other people using your internet? The fact it's a constant lag can mean bandwidth just isn't high enough. Netplay only adds about 20 - 25% more strain to a CPU than playing alone, so this is not normal behavior. Try finding other people to play with, playing with only two players instead of three; it's very possible someone's internet is just messing up and causing problems.
Super Smash Bros. Melee, Kirby Air Ride and Mario Party 5 have all been tested and verified to work no problem, so, I'm going to guess the problem is on one of the ISP's that you're playing with. If you need more help or it doesn't work out, keep me updated and I'll work with you more closely.
1: Mario Party 5 is kinda hard to run because the INI defaults EFB2Ram on.
2: Kirby Air Ride works in Dualcore, I haven't been able to desync. It's literally the second easiest game to run on netplay behind Mario Party 4; which also works on Dualcore.
With that out of the way, have you tried older builds? Netplay has gotten wrecked by half finished features and such as of recent. I'd heavily recommend trying something like 3.5-1789.
Are other people using your internet? The fact it's a constant lag can mean bandwidth just isn't high enough. Netplay only adds about 20 - 25% more strain to a CPU than playing alone, so this is not normal behavior. Try finding other people to play with, playing with only two players instead of three; it's very possible someone's internet is just messing up and causing problems.
Super Smash Bros. Melee, Kirby Air Ride and Mario Party 5 have all been tested and verified to work no problem, so, I'm going to guess the problem is on one of the ISP's that you're playing with. If you need more help or it doesn't work out, keep me updated and I'll work with you more closely.