Eh, when you quote my text, at least quote properly lah. Like, where did all the:
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go to?
SERIOUSLY.
Leave the 50-500 at home. Serious advice.
Leave the 1.4x TC at home. Serious advice.
Leave the flash at home. Serious advice, but bears explanation. Firstly, flash pictures look unnatural and overly harsh. Secondly, flash is unreliable in the given shooting circumstances, you will end up with over/under exposed pictures from one to the next. Thirdly, recycle time is too slow. Fourthly, you don't have enough juice to work with anything more than about 15m away. Doesn't matter what your guide number says, out in the field, there's absolutely nothing to reflect the light back, so your flash is severely "weakened" compared to normal. Okay, maybe a Metz MZ70 might get a bit more than 15m...
Leave the camera at home. Semi-serious advice. I'm not trying to deny you the joy of shooting sport, far from it. The problem is, you're faced with this situation. Flash, as explained above, it far from ideal. Non-flash, in your situation, is also far from ideal. I haven't shot at stadia back in Singapore before, but I doubt (although they *might*) have better light than the stadia I shoot at.
In the stadia I shoot at, EI1600 at f2.8 is stretching things. You're limited to an EI of 1000. Now you know why I say leave the 50-500 and the TC at home? You simply haven't got the light for it. I'm not even sure you'll have the light for the 70-200 by itself. Because I've shot at grounds where EI3200 with serious compromises in the shutter speed department at f2.8 still doesn't cut it.
But certainly, bring the camera and have a stab at it. I might be pleasantly surprised to find out I'm wrong about the lights. I'd bring the flash too in all seriousness. If the light is absolutely appalling... and I mean *absolutely* then that's probably going to be the lesser of two evils.
Good luck.