For GAMING SLI is not worth the hassle. For other tasks, okay, but when it comes to games, it would be a wise decision to get a SINGLE powerful GPU instead.
Games don't scale well on an SLI setup. It might help with some future Ray tracing games, but ONLY if the game's Engine supports SLI/NVLINK, and the game developers implement this feature in games.
ELSE, you would be just wasting the potential of one of the GPUs, and it will draw extra power as well.