I had to switch to Tasigna from Gleevec earlier this year. Never had stable MMR on Gleevec, and the CML apparently mutated sometime in the first two years. Anyway, I have had far fewer side effects from Tasigna than from Gleevec even on the full 600 mg/day (four 150 mg tablets). Don't even have to take Immodium AD anymore! However, the red blood cell count continues to be very low, and I end up having to take at least one nap each day. Gave up full time work even before diagnosis (I was then 59) and have not been able to do more than 10-12 hours per week, even on Tasigna.
Hope you can be successful on the lower dosage. Tasigna has really helped my quality of life, but there is no way things are the same as before CML. That's hard to explain to people, because they assume we are 'cured." Family members can get frustrated with us, so communication about CML is really important.