there are not much similarities, there's no point looking for difference. when RUP iterations are used - in whatever size projects  - in its task breakdown you will end up using agile anyway. size of the project really matters when choosing the process  flow. for instance when you mention enterprise project, is it large  scale? or do you only mean a multi-tier, but even so, when you look at the nature of enterprise you have to have an elaboration, cause it is within its nature to scale  overtime, therefore elaboration will become a key driver at project plan time. this will allow teams to have broader scope of thinking

size of the project always tells you what methodology you need to go for, and how much documentation is required. some people tend to follow academical and theoritical patterns who "may" fall into lot of costs problem but some use both theoretical practices with some level of experience.

what good you might gain from agile RUP , it depends if agile is going to be applied at high level or do you tend to use it at iterations? but keep this in mind that these practices are not written on stone, so you may produce a new methodology that creates more productivity in comparison to its competitors with less cost