R6 mk1 or R8? Which for low-light music photos?

[hueigh]

It's time for me to move up from my 5d mkiii. I don't have a huge budget and only very occasionally shoot professionally so I can't spend more than about $1500.
I shoot a LOT of low-light music photos, so I'm thinking IBIS would be a big benefit, and that would mean the R6 mki. But I've never had IBIS, so I'm asking for your help. If you were shooting a good amount of low-light music photos, which camera would you want?

[p4pictures]

This is indeed a tough one, and I'm tempted to suggest that the EOS R6 might be the better option for you. 

Firstly IBIS is a fabulous tool to reduce the effect of camera shake, but subject movement can only be avoided with fast shutter speeds. I can hand hold a 40mm lens for 1 second on my EOS R6 and have sharp shots, but anything or any person in them that is moving will be blurred. Shutter speed is the only fix for a moving subject. 

EOS R6 has AF that works in lower light than the EOS R6 Mark II and EOS R8, thanks to it's lower pixel count. However the difference is quite small. The EOS R8 is a super compact camera, but you do lose the 2nd card slot and the ability to use any existing LP-E6 batteries from your EOS 5D Mark III.