Is 0.4 GHz of extra processor speed worth €300? (about $430)
There is no simple answer. IMHO, the question is not about 0.4 GHz. (BTW, it is 17% above 2.3).

The real questions are:


do you have external USB or any other backup solution?


no - consider buying an external HDD first!
yes, I have - next question :)

have you already max. memory in your config?


no - consider investing into more memory first
yes, already max. memory - go to the next question

is there a config with better graphics performance?


yes - consider it first
no - next question

are you a heavy emulated Windows user (Parallels, VMware, VirtualBox etc)?


yes, go for the 2.7
no - next

do you need every millisecond of power (because of, for example, gaming, video editing, etc.)?


yes - buy the high-end one
no - next question

are you a bit paranoid (meaning, planning to use the FileVault encrypting for your $HOME folder)?


yes - buy the high-end one
no - next

how often are you upgrading your Mac?


every 18 months (one generation) - don't buy the high-end one, because usually they are a bit overpriced
every 2 years or more? - buy the high-end



misc. ;)


do you already own an iPad?


no?! - consider saving another 300 euros on notebook and buy an iPad - trust me, it is much better for browsing in the bed... ;)

is your girlfriend a technical geek?


yes - the high-end is a MUST! :)
no, bring her to somewhere for 300 EUR :)



misc 2 :)


Have iPad, no girlfriend - and have you decided to save 300 euros based on this answer? Consider sending me 50% ;) :)