Yes, you can choose to overpower, or not overpower a brass quintet with a given instrument, regardless of size. If you are a strong-enough player, you could probably overpower a quintet with a 3/4 Jupiter or Weril tuba. Conversely, you can (with awareness and concentration) choose to provide a foundation and good blend and balance in a quintet with a 5/4 tuba, or a sousaphone for that matter. If you can get the sound and articulation you want on a given tuba, and play reasonably well in-tune with it, don't worry about the rest - you'll grow into the horn.
To answer Doc, I did play a 5/4 Rudi CC regularly in a professional brass quintet for several years. I tried several other horns out on them, and they didn't like them as well. To reply to Mary Ann's post about getting all those complaints, "Whaddaya expect out of a pack of horn players?!"
I have a 1291. I bought it before the CC was available so it is a BBb with 5 valves. I play it in a brass band, wind symphony, orchestra, tuba quartet and brass quintet, among other things. I have found it to be the single most versatile horn I have ever owned. I play 1st tuba in one quartet and 2nd in another and the horn fits boths roles. In brass quintet, it can be played much smaller and lighter than its appearance would suggest. In orchestra, it holds its own. The CC is a bit lighter yet, so should be even less of a problem.
Most of us have been to things like Tuba Christmas and heard players who would overpower the massed band at a football standium on HS band day, but if one is attentive and plays within the character of the group, the 1291 will go along and not overpower yet rise to the occasion in a larger ensemble.
What lies behind us, and what lies before us are tiny matters compared to what lies within us.
~ Ralph Waldo Emerson ~