Different Cassette?

[Aggie_Ama]

Since others here ride a similar stock set up here is what I went with. I changed the 12-25 cassette to a 12-27 Shimano cassette. The LBS said Shimano doesn't recommend going to 12-28 probably just cause they don't make it but whatever. My goal was keep my Ultegra Rear Deraileur, giving me one more easy gear and keeping it cheap. I may end up looking into other options because I am pretty sure this won't be enough but I want to try it before dropping a lot of money. Right now I am only out $100 and have some more time to decide what I want.

Right now it only once a month or so that I get to enjoy these climbing quad busters, so it seemed silly to drop a lot of money on switching to a mountain set up. My budget was low right now because I am not completely ready to commit to changing so much.
My bike is now:
105 Front
Ultegra Rear
12-27 Ultegra Cassette