How common are 5' tanks (am looking for one)

[Reef Pilot]

Well, am still looking and no luck so far.

Have also heard/seen a few comments from an lfs and forums that make me wonder:

Was told by one person to avoid used glass tanks because the glass gets brittle over time, and will crack/break. Is this true? Also, the silicone will weaken and let go.

Acrylic tanks are better, because the joints are "welded" by the glue, and won't let go with time. Is this true?

Comments and opinions welcome.