NEED HELP. What wireless card do i get? AHHHHHH!!!!

I got a new desktop computer but it has no wireless card yet. Im looking for one that can give me at least 300 - 400 mbps. I know the wireless speed depends on your router, ISP, modem and other factors, but right now im getting an average of 300 mbps on my laptop. This is the one im looking at right now

D-Link Xtreme N DWA-556 PCI Express Desktop Adapter
http://www.amazon.com/D-Link-DWA-556...725932&sr=8-11

I need to get a card with a PCIE 2.0x1 slot because thats the only slot i have left on my motherboard. Amazon says the speed is only 54 mbps but i think thats on a or b networks. I think Ive read somewhere that this one can get up to 300mbps on a N network. Any help on my decision would be appreciated.

Are there PCI Express x1 cards that can go faster than 300mbps or is that only for PCI Express x16?

Mabey this USB wireless adapter would work better than a wireless card.
TRENDnet | Products | 450Mbps Wireless N Adapters | TEW-684UB

This adpater should have a rate of 450 mbps for uploading and downloading. The only thing is, I thought USB wireless adapters were less effective compared to wireless cards. USB adpaters are supposed to be convienent but not as fast, and PCIe cards are supposed to be harder to plug in but have better reception. How is it that this adapter can recieve at 450mbps if a wireless PCIe x1 card can not?

Ok I think im just about done researching and these are the two best choices I can find.
USB
TRENDnet | Products | 450Mbps Wireless N Adapters | TEW-684UB

PCIe 2.0(x1)
TL-WDN4800 - Welcome to TP-LINK

These both state they offer 450mbps and I cant find anyting that has faster rates. The choice is between USB or PCIe x1. USB should be more conveinent, and better reception(because its not blocked by the case) but wont be able to disapate heat as well or as long a range as PCIe. PCI should have better range and heat disapating ability. What now?