It sounds like you just have a problem with how outlook is configured,or with that installation.
Outlook 2007 really is a brilliant mail client; its fast, very reliable, with a great UI and its very customisable. Looking at your system spec you should have no problems running it at all..so I would suggest the steps below, or re-installing outlook as a worst-case scenario.
Who provides your email at the moment? The most obvious cause of your email being slow with outlook 07 could be that your using IMAP. IMAP is great in some situations (mainly for syncronising to allow online and offline access to email) however its terribly slow if you have a large amount of email or lots of folders...I would stab a guess that you used the auto-configure option for your email in outlook, and I know that for some silly reason outlook seems to default to imap in most cases if you use the auto-config tool.
So, I would first check that your email account is setup to use POP3/SMTP and *not* IMAP, and then see if things improve for you. After all, you (or your work/university) have spent money getting outlook 2007 so it would be a shame to waste it.
The email provider should not make a difference to how fast outlook runs - so you'd have no real advantage to using gmail..unless you wanted to use the web interface for it. Personally I've been using Gmail since it first started and I love it - the fact that mail is never deleted is brilliant..excellent for finding old emails that I would otherwise have deleted by mistake