Just checking if that's normal, or I can optimize better?
Comparing daily income or even round reward isn't good enough, because there's many variables involved, like short-time pool luck, total pool hashrate etc. You should focus to your hashrate; more is better.
I use stratum with OpenCl miners on GUIminer version 2011-05-01 since I felt that this one worked the best.
Please use latest GUIminer, not that 2011 version. There are known issues in this version.