http://www.rtings.com/tv/reviews/samsung/ku6300
That reviewer says it's 10 bit, but like you said, no wide color gamut.
HDR mode in games look a lot brighter and prettier to me, but I imagine real HDR is much much better.
I was on the same boat as you and it's why I bought it. At 40" the next cheapest/good option that displayed true HDR was nearly $700 (ku7000) at my closest Best Buy, so basically over double the price of the ku6290 just for true HDR. So I decided to get the 6290 as sort of a stopgap till HDR tech matures a bit more and prices come down.
Not true HDR no.
It's Costco tho, you have 90 days to return it if you decide it's not worth it.