My iX arrives in about 4 weeks
On the price - the 50 is priced quite high but a larger battery and 500bhp justifies that.
Legroom - there is much more of this in the back than in the Y
Plus, it’s built much better.
My last 9 cars have been BMWs, and I have never liked teslas, so believe me that my view isn't biased because my wife owns one! I went into driving it wanting to like it other than the looks, and in truth i did, but it just feels more like an X3 segment car with regards to the build quality and interior space.
It is (quite notably) slower than the Y with a similar range so the cost doesn't justify it on that basis alone.
There absolutely less room in the back of the iX, even if on paper it has more. I verified this last night by literally getting out of one and in to the other with the driver's seat set up the same position for me to drive it. The major difference is that there is a lot of space under the seat to put your legs on the Y, it's truly remarkably spacious for how small the footprint is.
It is a little bit better built, but definitely not "much" better, the door closing etc is worse than my g30, and there are some odd bits that feel cheaper. The seats don't have as much support as my car or an x5, which surprised me... actually more similar to. Tesla seats albeit definitely better. The proper dash is much nicer yes, and definitely having air suspension makes a big difference to the ride quality. The tech is better too.
In summary, I'd happily put 15-20k of value on the iX over the Y, but at 50k more the iX misses the mark massively from my 250 miles in it. It's a good car but it's priced like it should be x5 / x7 quality and it's not - the new i5 is a much much nicer place to be when you're spending that money!
This is just my view though, and I'm sure you won't be put out by it!