Any chance you can use an SSD in the server? That client would make a good server too.

RAM isn't a big deal. I used 5GB in my test with a full production database. 1000+ messages in the inbox. 10 years in practice with AC.

10K RPM HDD's only have IOPS in the 125-150 range. SSD's have them in the 60K+ range. Most likely AC just needs more IOPS to run. You can either RAID HDD's or get an SSD. I used a <$100 Kingston 256GB SSD. Beats the $2000-$3000 SQL upgrade people are recommending.