I'm trying to compare two normally distributed data sets that have roughly equivalent standard deviations (at most a factor of 2 different). I'm using the T test to determine a statistical difference between these populations but the p value being returned is often on the order of 10^-200 or smaller. Each data set has 300 elements so there are 598 degrees of freedom. I've read that large data sets can lead to a Type-I error, showing that there is a very significant difference in some small parameter. Can anyone suggest a way to show a statistical difference between two large populations that avoids errors?

Thanks,

Dan