hey
i don't belive removing your modem or any other pci card would help, and as far as i know each pci slot is dsignated like usb. you wouldn't really speed up your video card. what is the brand and wattage of your psu? the onlt problem you could potentally have is voltage and that wouldnt nessicarily speed up or slow down your video card. i would leave every pci card in that is in. last question do you have a microATX board or standard board(how many pci slots do you have total??)