Building new computer, ATX vs MiniATX?

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?

Newegg has four mini atx cases that ALL take regular ATX mobo's...So no space savings as far as I can tell...Just a drasticlly small selection to choose from.

Keep in mind if you go too small you get into the land of needing low profile video cards etc....

The main thing you lose out on with mini-ATX are expansion slots. Remember that most decent graphics cards are double width, so that's two lots right there. Personally, given that you need a fairly high-end PC for your uses, I'd tick with ATX.

I would advise going with the Core i7, but then I've just ordered all the bits for my i7 build, so I would say that :D