Iphone x AT&T GSM version same as the SIM free GSM version?

Hey,

I'm coming home to the states for Christmas from Europe. I've been wanting to get an Iphone X to take back with me. I ordered the AT&T GSM unlocked Iphone a couple weeks ago to make sure I would be able to get one (hoping I would be able to put my SIM card in). Now I see Apple is selling it SIM free, so I know my SIM card would work. Are there any differences in the GSM in both these phones? I've heard that the GSM is better in the AT&T phone for Europe than the SIM free one with both GSM and CDMA. Everything I can find on the web shows the same specs for GSM on both Iphones. Since it's such an expensive purchase, I'm looking for any help on the knowledge of this question.

Thank You.