I want to build another computer that will be used for gaming, watching HD movies, listening to music, 3D modeling, image manipulation, and so on.

My current system is:

nVidia nForce 780i 3-Way SLI 1333Mhz LGA 775
OCZ GameXStream 700W PSU SLI Certified
Intel Core 2 Duo @ 2.66Ghz LGA 775
nVidia GeForce 8800GT OC 512mb GDDR3
Seagate Barracuda 7200.11 500Gb SATA-3 HDD
LG DVD DL Burner

My system is ATX factor. I want to go with MiniATX this time. Are there any drawbacks of building a computer for such purposes with MiniATX motherboard? Is it better to go i7, i5, or get a Core 2 Quad @ 3.XGhz?

The main point is to get a newer system, with smaller dimension, that will have more juice than my current system. Is it possible, or am I dreaming?