Plasma cannons of any type are practically invisible on the lowest graphical settings. The most I ever see are a couple of tiny white dots at certain camera angles. All the other energy types are visible at this graphical level, the only thing I haven't lowered is the half resolution option.
The Somraw, K'tinga, D'Kyr, D7, Kumari, Xindi carrier, Xindi escort, and the T'Varo are all older than the Constitution Refit and yet they are tier 5. The Constellation is made up primarily of Connie refit parts and it is tier 5, there is no logical reason whatsoever for the no tier 5/6 connie rule.