I tried 30 lb. Fireline with 12 lb. Trilene mono for the leader a while back, and it was a nightmare. I did get the desired added sensitivity, but that was heavily outweighed by the drawbacks:
1. When my egg sinker got hung in rocks and/or brush, the Fireline was too strong to break. It was either let the line cut my fingers off trying to break the line or troll all the way back to where the line was hung. Still couldn't get it loose half the time and had to cut the line.
2. Every hook set, the mono broke at the hook. At first, I thought it was because I was setting the hook too hard. The last few times, I barely put applied any pressure at all. I emailed Pure Fishing, who makes both lines, and they didn't know what the problem could be. They finally said it could be a bad batch of Trilene.

After that trip, I went back to using 20 lb. Excel for the main line and 12-14 pound Excel for the leader. Not as sensitive, but at least I could hook and land a fish.