hey, i have i5 7400 kaby lake..socket lga 1151..which gpu is the best..
He might be thinking about how PhysX could be performed on a 2nd card, even if they weren't the same. At this point, I've not heard of this being a possibility, and let's just be honest, it's not going to be worth the money, even if it did.Pair a GTX with an RTX? No. I don't ever see that happening. NVidia has always been very restrictive on what will SLI together.
Up until super recently they were't even going to allow GTX cards to do ray tracing. They changed their mind recently. I'm not sure they opened up ray tracing and SLI. Considering SLIs performance recently if I were you and looking to do ray tracing I'd be focused more on getting the best RTX card you can. I strongly suggest waiting for Ray Tracing games to show up however. So far there isn't much you can do with it.