So you want to feel "upgraded"... ok
How does an extra 100 horsepower, and accelerating smoother than sex, sound?
I love the e60 5 series too. they're great. And if you're not an aggressive driver, but DO feel the need to carry more people or shit, get the 530.
If you drive hard, get the 335i. You will feel post-coital (like you feel after sex) everytime you get out of it.
Plus, you'll get some cool stuff like real time traffic monitoring.
You're on a 3 series site. don't expect many people to try to sell you on the 5.
Matt