Question: A year ago I advise a user to move off files from e-mail to shared storage as the PST file sizes were a concern and PC was running Outlook slowly.

The 3 PST files have grown when i gave the initial advice from 20GB, 28GB and 14GB to a huge size which is now 48GB, 49GB and 10GB.

Performance of the PC is really suffering and continually hanging in Outlook.

PSTs have been scanned and had all errors corrected with Scan PST.

Have advise user again to move large attachments in emails out of the PST and in to shared server storage.

User is asking how to fix the PC and we have tried everything - sincerely i believe this is an issue with huge file sizes related to large attachments.

1. Has this exceeded the capability of Outlook 2010?
2. Any other recommendations?
3. Any useful links to educate users on file sizes which work well, and
sizes that should be avoided?

Answer: 
I can only assume they are making changes to the attachments and sending them back and forth to each other via email thus numerous copies of similar data is maintained.

I suggest not doing attachments as much as possible and instead use cloud alternatives. For example, Google Drive. Using Google Drive you may share the same file with numerous people and control what permissions they have. Just announced at Google IO, a business service for unlimited storage for $10/month. Additionally, basic free account still offers several GB for free. For 1.99/month I upgraded to 125gb of google storage.

The only things that will make outlook happy is if you add tons of memory 16gb or more to start and/or either compress or decompress the PST files. It will have to actively decompress it so that could harm performance.

Having more PST files and spreading out the load could also help. Have an archive PST file and anything more than, for example, 1 year old goes in there. In fact, having 1 for each year would be a good idea. Accessing the archives will be slower, but active work will be faster.
Two of your PST files are approaching the preconfigured file size limit in Outlook 2010. You should look into splitting these large PST files into smaller PST files.

<http://support.microsoft.com/kb/982577>

If you're using Exchange Server 2010 or Exchange Server 2013 as your email server you should consider creating an Archive mailbox for the user and importing the PST files into the Archive mailbox. Note that this requires an Enterprise CAL for Exchange (AFAIK).