Wrestling and Muay Thai.
Wrestling (Clearly, you have enormous strength for your size, etc, etc. Good ground and pound)
Muay Thai, Your run, Good strength in your legs, you'll have a great grip due to wrestling and the strength will make it all the better.
Best combination, in my opinion.
As long as you can hold your own on the ground (e.g. not let some BJJ guy overpower your joints and rip your arms off[/hyberbole]) then you'll be great with those two.
Muay Thai and Freestyle wrestling are my main styles, and its so easy to change through stances/mindsets. My personal rules are as follows:
If they're far, only do short kicks and do high kicks as least as possible(I learnt it from reading Bruce Lee's views on realistic fighting, for conservation and low risk moves).
If they're medium, chok/sok/kao (punch/elbow/knee). The blatant, but you'll be surprised how many dumb street fighters don't know what a knee is. Especially in New Zealand.
If they're close and clinch fails then double leg takedown, head and arm, side takedown, then GnP! GnP! GnP!
However I haven't had any official fights inside a ring/octagon because I'm too young. They work when some dickhead is trying to pick a fight with you at a party or something.
Edit: And what the hell 50kgs and you can bench 130kg +?
My anus you can. I'm 5"10 90kgs and I struggle with 100kgs.