256 MB is a scam, don't buy it.
AGP 8x is equally a scam, just a cheaper scam.
To expand what I mean:
1) Only like, three games in existance utilize 256 mb RAM, and even games coming out soon (namely Half-Life 2) only use up to 128 MB. 256 MB is simply to make your e-pen0r look bigger to yourself: Everyone else is laughing at you. And by the time 256 MB RAM is mandatory, you'll need a bigger beefier card by then anyway.
2) AGP 8X is like using a broadband connection to download files from someone hosting them on a 56k: You're only going to go as fast as them.
To make it more clear, imagine AGP are lanes on a road going in each direction. AGP 4x is 8 lanes, 4 in each direction. AGP 8X is 16 lanes, 8 in each direction.
Now, on that road are cargo trucks. They're hauling data from your card, down your AGP freeway, and to your CPU, where they head back.
Unfortunately, what you're never told, is that both the card, and the software running, can only put out a certain number of cargo trucks.
At AGP 1x, your trucks are going to get slowed down. They all can only drive in one lane, and get backed up easilly.
At AGP 2x (two lanes), your trucks can pass each other and generally get there quicker. However, backups can still happen, especially if you have lots of trucks on it.
AGP 4x (four lanes) is ideal. If a backup happens you have many more lanes to get around it. Each direction has enough room to manuever around and get there quicker, through fast lanes, slow lanes, etc. 4 lanes will work just fine, and would require a large backup to cause trouble.
AGP 6x (six lanes) is great. It's your basic freeway. Lots of space to avoid congestions, 6 lanes in each direction is enough space for even the most trucks you can send out.
AGP 8x (eight lane L.A. Superfreeway) is stupid. Why? Because putting in a 16 lane superfreeway is pointless if you don't have traffic to fill it: and you don't. Your card isn't going to detect 8X AGP and suddenly decide to work at double the power to fill all that space with cargo trucks. It's still going to send out the same number. You have lots of room, but no where near as many trucks to fill all the lanes. All your trucks have plenty of space, they won't get backed up (but they don't get backed up on 6x either, so it's just redundancy). Until you actually have the capability to fill every lane of AGP 8X with trucks, it's an utter waste.
The worst part is, both AGP 8X support AND 256 RAM are utterly POINTLESS, but they cost a flipping FORTUNE. However, it makes sense: Idiots buy them for bigger numbers without understanding a damn thing - These are the same people who buy Alienware computers who use Pentiums because they have 'bigger jiggahurts!'