Lets say you were approached by a group of investors with capital, of up to $500k. They wanted a return of 150% minimum, so $1.25m+ in revenue per MONTH. It's a JV and you make 5% of revenue over $1m.
What would you do?
What offer would you run & what ad networks? What offers can scale to that level & get ROI like that do you think
I would say thanks and bye.
With $1.25m it would be even 250% return of your $500k and this is not realistic to achieve stable and guaranteed.
@twinaxe makes excellent point 
Just for fun though... I suppose if I had to try to spend 500k per month on one offer profitably... I would do a combination of natives and facebook. There's definitely a few folks who spend 500k/mo (17.5k+/day) on a single offer on Taboola/Outbrain (although I'd guess not more than a small handful at most), and I imagine there's people who spend that in a few days on Facbeook...
Google Display and Youtube would be possibilities too... but Youtube seems more congruent with webinar funnels and stuff like that...
Would definitely depend on the type of offer too obviously as some offers would do better on some networks vs others 
Edit: And it seems most of the biggest media buying outfits with huge volume use everything in tandem - facebook, youtube, gdn, natives, search, etc, as each feeds into the other.
this type of budget would be better off if you owned the backend such as your own eCom offer /