Mini Z > Xmod.
Following is opinion, not fact.
Xmods are NOT hobby grade. Personaly having owned one it had a rediculous amount of slop in the steering, it was not quick really either. Handling was poor, speed was poor, parts quality was poor. To just get it to "hobby" standards I'd have to have had put way too much into it to get it to feel "real". I cannot deny that I did have ALOT of fun with it though in my basement.
I sold mine for way more than I bought it for, and original black skyline though.