Ah just realized that I meant to say this was done in crop-mode. (and stretch it in post)
<--- again I forgot that when using crop-mode during slo-mo's (48,50,60fps) it would automatically cut down to 30fps which is what got me somewhat thinking that 50p 1080p was 'possible' for a second after reading this post. Sorry about that! 
As far as I can remember on top of my head but will double check once I get home this weekend from work.
My fault on that guys!
*EDIT*
Even more so embarrassing... I was wrong once again.
I guess what got me confused was the fact that I thought it would have been a lot more than just a few seconds (per @Taranis's comment) for 50p in 1080p.
it actually has been awhile since I've used this.

However, here's the update:
1920x672 (stretch in post to get 1080 -
16:9) gives me
12-13 seconds in 50p with GD off, Card warm-up, Preview AUTO & Small Hacks.
1920x646 (stretch in post to get 1038 -
1.85:1) gives me
16-17 seconds in 50p w GD off, Card warm-up, Auto Preview & Small Hacks.
1920x598 (stretch in post to get 960 -
2:1) gives me
30-31 seconds in 50p w GD off, Card warm-up, Auto Preview & Small Hacks.
1920x544 (stretch in post to get 872 -
2.20:1) gives me
continuous recording in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
_______________________________________________________________________________________________________________
1856x650 (stretch in post to get 1044 -
16:9) gives me
19-20 seconds in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
1856x624 (stretch in post to get 1004 -
1.85:1) gives me
28-29 seconds in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
1856x578 (stretch in post to get 928 -
2:1) gives me
continuous recording in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
_______________________________________________________________________________________________________________
1792x628 (stretch in post to get 1008 -
16:9) gives me
39-40 seconds in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
1728x606 (stretch in post to get 972 -
16:9) gives me
continuous recording in 50p w GD off, Card warm-up, Auto Preview & Small hacks.
This was all done on a KB 128gb x1066 CF card.
Hope this helps!