Re: pci express?
PCI-E (pci express) is what you want as it's the fastest slot. PCI is slow these days, PCI-E express can (apparently) offer 70 times the bandwidth of PCI. PCI-Ex16 should/could be written like PCI-E x16. There are different slot sizes and x16 is generally what is used for PCI-E graphics cards. There is also x4 x8 ( i think there is a x1 which would explain PCI-Ex1).
1: Q6700 @ stock 3GHz 775 6GB-DDR800 ASROCK penryn 1600SLI, 1GB ATI RAEDON 5770 ~ 3TB internal;
2: 3.2Ghz Phenom 9550 Black ed 4GB-DDR3, ASUS skt AM3, HD 4850 512MB
3: Core i7 3.2GHz, 6GB DDR3, 512MB EN8800GT, 1TB Internal
4: Athlon 4000+ skt 939 6600GT 3GB
5: P4 3.4GHz, 3GB-DDR, ASUS skt 775, ATI RAEDON 9550
+ all my other lovely comp parts :)