Optiplex 990 MT CPU & Memory

What is the max i7 I can use?

Has anyone successfully used 32GB (8GBx4) in a 990MT?

Any suggestions for other brands welcomed but I am looking at one of these from Crucial:

Ballistix Sport BLS8G3D1609DS1S00:

DDR3 PC3-12800 • 9-9-9-24 • Unbuffered • NON-ECC • DDR3-1600 • 1.5V • 1024Meg x 64

Ballistix Tactical BLT8G3D1608DT1TX0:

DDR3 PC3-12800 • 8-8-8-24 • Unbuffered NON-ECC DDR3-1600 1.5V 1024Meg x 64

Ballistix Sport BLS8G3D169DS3:

DDR3 PC3-12800 • 9-9-9-24 • Unbuffered NON-ECC DDR3-1600 1.5V 1024Meg x 64

Ballistix Tactical BLT8G3D1608ET3LX0

DDR3 PC3-12800 • 8-8-8-24 • Unbuffered NON-ECC DDR3-1600 1.35V 1024Meg x 64 Low Profile