Not sure about the A7Sii but the "top private dealer" you spoke to is wrong. The A7Rii will overheat but only with extended video recording in UHD. I own one and I would challenge anyone to find a single unit that doesn't overheat. Having said this, most users won't notice it because either they use the camera for stills or record shorter video clips. Our unit overheats in 80°f weather on average at around 25 mins.. We do extended interviews and like the A7Rii for its small size and versatility in the field when we don't want to carry our FS7s. We use a Shogun which eliminates both the overheating issue and the recording time limit restriction.
Knuck got a reaction from kaylee in Sony A7sII - Overheating in 4k?