Here is yet another paper about the star clusters in M83!
It was just now published in the following reference:
(2014), Astrophysical Journal, Volume 787, page 17
The preprint of this paper can be obtained at this webpage:
http://arxiv.org/abs/1406.1157
I strongly suspect that the most luminous of the young star clusters in M83 may actually be glimpsed in visual observations with amateur telescopes;
Thim and Tammann and Saha and Sandage, in 2003, used Cepheid Variables to derive a dereddened distance modulus for M83 of 28.25, implying that this galaxy is at a Distance of 4.5 Megaparsecs (= 14.7 million light years)
Applying this Distance and Distance Modulus correction to an overluminous Young star cluster in M83 with a luminosity of Absolute Visual Magnitude minus 13 .........
implies an apparent visual magnitude of 15.25 for such a very luminous star cluster!
Added in edit:
The star cluster R136 (in the LMC), which is the most extreme young star cluster that has so far been discovered in the Milky Way and the Magellanic clouds, has a luminosity of Absolute Visual Magnitude Minus 11.7, and it weighs in at very roughly 60,000 solar masses.
This star cluster would be near to visual magnitude 16.5 if it were in M83, and, statistically speaking, it is likely that M83 (a much bigger galaxy than LMC) will have a few clusters that are brighter than R136
The galaxy M31 has a young star cluster known as
VdB0 that is absolute visual magnitude minus 10.0 (probably the most luminous Young cluster known in the Andromeda Galaxy), and if I assume the modern compromise distance estimate for M31 from multiple measurement techniques (m-M = 24.4 and 760 kiloparsecs), this cluster could be brighter than 15 magn. in the telescope!
The reference arxiv 0812.1668 gives a measured V magnitude of 14.67 for VdB0, so it seems that I am not too far off in my reasoning.....