Mega bits per second. Divide it by 8 to give you mega bytes per second. So that equates to 6.75 MBytes per second. That is a lot faster than your connection abilities can cater for. 512 kbps = 64 KB/s (minus over-head loss in reality which ranges between 10-20%) which will probably equate to around 50-55 KB/s

Now ethernet speeds depends upon the ethernet cards in your computers. Normally 10 Mbps, but you can get up to 100/1,000 Mbps. I have all 3 on my mac but only use 10. I think the faster ones use different cable afaik. I'm not much of a knowledge on networking.

There may be other issues concerning wireless such as interference or distance between nodes. AFAIK All wireless devices have built in firewall such as NAT which is arguably a type of firewall. I can't remember much else about the ethernet speeds.

But I'm not qualified to answer your question about which is better. Wireless would certainly save you the cabling issue if you have the computers in different rooms, etc. (such as like mine are lol )