SLI is dead, don't waste your time.
Actually I have SLI. People like to say it is "Dead", but that is far from correct. I agree it is best to buy the best single card you can afford, but if you happen to have a GTX1070 and come across on a great deal on another GTX1070 then it will payoff for most.
Example of some games: Far Cry series, Apex Legends, Tomb Raider, The Witcher III, Dirt series, Battlefield Series, Frostpunk, Rainbos Six Siege, Grand Theft Auto V, Dawn of War, Deus Ex Mankind Divided, For Honor, Ghost Recon Wildlands, Civilization VI, Strange Brigade, The Division 1 & 2, PUBG, Fallout 4, Sniper Elete 4, Watch Dogs 2, Ashes of the Singularity, Just Cause 3 & 4, Call of Duty (including Black Ops 4), Prey, Project Cars 2, Middle Earth: Shadow of War, Destiny 2, Total War: Warhammer II, Gears of War 4, Metro Exodus, and
the list goes on. (Just under 1400 games on the list. Both old and new)
Do all game support it...no. But it is not dead. Heck it doesn't even need a defibrillator. And when it works 2 GTX1070 in SLI typically outperform a RTX2080TI. I still remember the many comments "PC Gaming is Dead", yet here we are still gaming on our computers.
Signing off to go play the latest Madden (2020) that was just released...and yes...it has SLI support too
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Edit: Don't want this to derail this topic with the above. But IMO that is a part of "features" on a motherboard, and one that I personally look for over WiFi, etc. Easy to add Wi-Fi or 10Gb nic, but doubt you can add SLI support if you want it.