Found another great site; this one with all the commercial releases of games and the eprom size. It is confirmed that super tennis, fzero and super mairo world use two 256kb roms (most likley to save cost from one single 512kb unit)

http://www.solvalou.com/subpage/arcade_roms/S/nss_smw

27C256 is the eprom chip; no idea about speed.

nss_actr
Act Raiser (Nintendo Super System)

nss_adam
The Addams Family (Nintendo Super System)

nss_aten
David Crane's Amazing Tennis (Nintendo Super System)

nss_con3
Contra 3: The Alien Wars (Nintendo Super System)

nss_lwep
Lethal Weapon (Nintendo Super System)

nss_ncaa
NCAA Basketball (Nintendo Super System)

nss_rob3
Robocop 3 (Nintendo Super System)

nss_skin
Skins Game (Nintendo Super System)

nss_ssoc
Super Soccer (Nintendo Super System)

nss_smw
Super Mario World (Nintendo Super System)

nss_fzer
F-Zero (Nintendo Super System)

nss_sten
Super Tennis (Nintendo Super System)

Are all the commercial released games for the NSS/Nintendo Supser system. The biggest ones use a 512kb eprom, and most smaller ones use 256 as stated above.