SE One also limits you to two CPUs.
you can squeeze a LOT out of two CPUs if you know how to architect but if your PHBs think you have to have quad (or more) you need full standard (or enterprise).
FWIW, "one" is purely a pricepoint, not a product. when you buy it the CD pack is the same one you get if you order enterprise (other than saying "one" on the label) and when you run oui you get the options of installing enterprise or standard but nothing about "one". finally, they'll tell you that you have to use SLES or RHAS but if you just put the following in /etc/UnitedLinux-release:
UnitedLinux 1.0 (i586)
VERSION = 1.0
PATCHLEVEL = 3
it will install on any distro (assuming compatible glibc, etc.) though I would reccomend SuSE Professional (I know that works).