In your quest to find lower gears, don't forget not to overshoot your derailleur wrap capacity. Here's a good article:
Sheldon Brown's Bicycle Glossary Ca - Ce
In nutshell, be careful with just adding larger cassettes without considering whether your derailleur can handle the range. While a RoadLink will help the derailleur reach larger cogs, it doesn't help with chain wrap.
I have used a cassette with 42t cog (to climb Pikes Peak), but I had to lock out the big ring in the front to make sure that I didn't exceed chain wrap limits.