MOTUnation.com

I need more power for rendering video - $3K is total budget

would love to stay portable, but if the tower is twice the power of the laptop I'd go that direction

so how does an i7 Macbook Pro compare to the entry level Mac Pro?

(strictly horsepower - not comparing I/O & expansion options)

Go here http://www.everymac.com/ultimate-mac-comparison and select the models, it will give you a side-by-side comparison. It will also give you their Geekbench scores.