I'm absolutely amazed that with modern GPU's there is no standard for supporting them properly given that they're heavy enough to damage the motherboard slots, or worse themselves. There is a youtube channel of a guy who repairs things like GPU's and the number of 40 series cards he's seeing that have the same basic issue where they're cracking along the connector into the motherboard is depressing, especially given that the motherboards have tended to go with reinforced slots to protect themselves from the weight, but the cards that are now hitting ~£1500 have no such thing.
As has been said repeated, an anti-sag bracket or one of the various support risers that you can put under the card are a must these days.
I was joking to my brother when I built his machine in November that the old Globalwin 802's were decades ahead of their time, they had the option (an extra fiver) for a "riser support" pack, it was a bar that you slotted into the case once you'd fitted the cards and it had a variety of different length supports that you screwed in to support heavy cards.