Wait for the new cards to be out and for people to start testing them, including in multi GPU configs.
Nvidia don't usually send out cards to be SLI performance tested but reviewers sometimes loan each other review samples to get it done I think.
It's likely that the adage of getting a single, more powerful GPU being a better option than a pair of less powerful ones, will still hold true. Multiple GPU tech is certainly not all that widely supported - it's hit and miss at best. And on top of all the old multi GPU complaints, AA techniques like TAA, which is very popular in modern AAA titles, exclude its use too.
Not to mention your context too. Your monitor, resolution, refresh rate, adaptive sync tech. And what games and framerates/settings you're aiming for. As well as your budget.
And the pricing of the GPUs. And how they perform. Which again comes back to the fact that we won't know until they're reviewed by independent tech media.
So I wouldn't consider anything until we know
I'd probably also wait for Zen 3 CPUs.