The wifes from Ukraine and we've done the trip before but my god that kind of driving is tedious if you just sit on the motorways. The roads in Romania (and no doubt onwards/around) will be sketchy. I'm not talking "oh theres a pothole" but donkey + kart, random steps up or down in the road surface where 2 different sections meet, questionable roadside services/fuel quality etc.
I'm sure a 335D would be capable but try and properly plan out a route so you can get a good estimate of fuel/toll costs before deciding, and remember you may want to alter it to take in some landmarks along the way.