My current systems are buckling under the load of Autocad LT 2012. While they have great multi-core processor speeds, their single core speeds are not up to snuff. AC LT 2012 does't utilize multiple processors. The current iMac was originally released with 10.8.4. Currently it comes with the latest 10.9. Apple has told me that it will not run 10.8. I find that hard to believe. Has anyone recently purchased and downgraded the os? Other wise it adds $1200 to the cost if I upgrade auto cad. Thanks in advance.