Exchange Server 2010 / Outlook 2010 Questions

I have exchange 2010 SP1 Roullup 4  - Here is the version reported in my Exchange Management Console - Version 14.1 (Build 218.15). 

Outlook clients are 2007 and 2010 running on Windows XP SP3 and Windows 7 SP1

Here are two issues i need help with

I have Google Postini handling my SPAM control and mail filtering and DO NOT, for any reason want to use Exchange internal message filtering mechanism!... So i setup the following:

Disable Junk Mail control in my outlook clients - is there a way to permanently remove Junk mail folder in Outlook Client?. I find a way to do this in exchange for OWA client 

Setup SCL to 0 and -1 on my HUB Transport, so that my HT will consider all email passing through not to be SPAM 

But I am still looking for an absolute solution or a way to confirm Exchange will not deliver any email coming into my organisation to users Junk mail folder in Outlook or permanently remove Junk Mail folder in Outlook client.

Second issue

Some of my Outlook client users (Outlook 2010) have their OST file grows between three to five times the size of their actual mailbox size on exchange when they are set to cache mode (either with download share folder option selected or not).

I understand the OST may probably be bigger than actual mailbox size but having the size between 3 to 5 times bigger than the actual mailbox size on the exchange server does not sounds right!

Here is  example: User A have Exchange Mailbox size = 4GB, but when in cache mode, outlook OST file size is 22GB