Third party COM and Outlook Extensions have a habit of creeping into Outlook - and these often cause stability issues. Many of the Add-Ins are not needed but still load themselves and impact all Outlook Profiles. Older versions of antivirus plug-ins and the Apple Change Notifier are examples of Add-Ins that can have an impact. It may be worth considering disabling some of the Addins and Extensions under Trust Centre.
In terms of Outlook integration, MailEnable is trying to go as close to providing the equivilant of the Outlook/Exchange experience (and as far as we are aware the Outlook/Integration we provide is superior to the synchronization/plug-in approach adopted by other vendors). The last release of MailEnable's connector for Outlook (1.40) is much better than earlier versions - and 1.41 is even better again. 1.41 can be downloaded from http://www.mailenable.com/mesetup141.exe
(32 bit Outlook) and http://www.mailenable.com/mesetup141x64.exe
(64 bit outlook) and will be released shortly. MailEnable is really committed to progressing this integration because its a clear differentiator. Newer releases are getting much faster and we are continually improving the stability (as mentioned, in many cases stability issues arise from integration with plug-ins that behave unusually - we of course sometimes have bugs of our own;-)). If you experience instability with the client, we would appreciate any feedback via the defect reporting section on the mailenable web site.
I agree with your opinions on Thunderbirdthunderbird+lightning(calendar)+ldap for Global Address List, etc... It is possible to obtain some of the key features of Outlook, but the end user experience is not comparable. I am sure once you commit to using TB/Lightning and forget the Outlook experience that it would be more palatable (coz the major features are there - it's just that they are fragmented - particularly from an installation/account setup point of view).
I will be interested to see what your experience is with Evolution, since I have not used it extensively.