XGBoost validation for number of trees

Question

I have a simple Question:

I am using XGBoost to classify some data: 1.) With 100 estimators I have following scores(roc_score): train_data : 98.5 validation_data : 97.2

2.) With 500 estimators I have following scores(roc_score): train_data : 99.4 validation_data : 97.7

Acco. to above can we say model with 500 estimators works better. Or should I change the validation data few times and see if similar kinds of increment happens by shifting from 100 to 500 estimators.