Hi Luca,
We can rest assured that the IGI report is not going to be taken seriously by the trade- or pretty much any serious buyer. Only GIA reports are used by serious trade buyers today.

In terms of  price: this type of stone- that being a "cape" color round- won't trade at $50,000 in any market I can think of.
I'm sure it's a beauty- and has a lot of value.
How much? It's not possible to say without seeing it.

HI Luca,
We had to remove the link as we don't link to other sites selling diamonds....

But I stand corrected- there are sites asking high prices for such stones.
Having said that, I don't think they'll find buyers.

Great points OMC!

We bought a lovely stone today- GIA graded U-V Si1- with an EX cut grade.
The difference in the asking price to what the cutter accepted was huge.
We'll be offering the diamond for $$2699.
He wanted a price that would have made our list price about $700 higher.
I'm not saying he was wrong- it might be worth $700 more- but my point was that the value is more affected by what people will be willing to pay for such stones.
To me that makes them a huge value.

More relative to the price: I just did some online checking and found 5carat+ J color stones for about $70k+-

An N color is worth substantially less than a J- I'd say about 30 % less

So it actually might bring $50k retail- but that means a private seller will get at least 30% less than that.