Well, I gave the speech this weekend. I think it went very well, so thank you to everyone who gave honest advice. After thinking back on other such speeches I've heard in the past, I realized that many tend to over-emphasize the closeness or significance of the friendship between the speaker and the bride/groom. Instead, I aimed to discuss how wonderful the bride is and only discussed our friendship as a vehicle to achieve that (i.e. talking about how much she's always been there for me, etc.). I also wanted to make sure I put enough emphasis on the quality of the groom, so I made a concerted effort to not just to brag about the bride.
People seemed to like the speech a lot. A couple dozen or so approached me to tell me how moved they were. The father of the bride came across the dance floor to hug me right after I finished, which meant a lot to me. Very glad it's over!