Which Apple Computer Is a Better Purchase For Heavy Video Editing, Graphic Design, and Music Production?

First off let me say I don't want any BS answers about how I should get a PC and save money. I like Macs, so this question is seriously about Macs.

So my current Late 2010 (Or 11) Macbook Pro is not powerful enough to run high resolution video or fps from my GoPro, as I don't have enough processing power. So my mom said I could look into saving up for a new one.

So for the tasks such as the high resolution video editing, graphic design, and music production, would you recommend:

iMac with 5k Retina Display
With 3.5 (Turbo up to 3.9 GHz and 16 GB RAM

$2,499.00

or a new laptop such as:
Macbook Pro 15" With Retina Display
With 2.9 GHz (Turbo up to 4.0) and 16GB RAM

$2,699.00

Please I'd like input on which is a better purchase.
I already have a Macbook Pro 13"

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