Your real problem is the BCD of our crank. I believe it is 110mm so you can't install anything less than a 34t. Well, I think technically 33t, but finding that is pretty much non-existent.

What I think you should do is run the ratio/speed numbers to see what advantage you will get from going to a wider range cassette and a longer cage rear derailleur, or swapping the crank to a 46/30.

I think a lot of people see a couple tooth change as their saving gear ratio and then find it is not as significant as they had hoped for. Running the numbers, especially with a cadence/speed calculation, may help you get a feel for how much benefit you will gain.

John