Most individual ships will be hard-pressed to survive in a C-5 site - say, Instrumental Core Reservoir - without other ships on hand to divert away firepower. Sleeper DPS is high, something like 1000 DPS with 18,952 per volley. The more ships to bear the load, the better.
For an individual, divide however much of your EHP you can afford to lose by 1100 or so, then multiply the result by your DPS. That is how much damage you will do to 1 enemy ship. Warp out, repair, and warp back to kill another; it is very hard to complete a C5-exclusive gas site in 1 ship. Ships like the Paladin will be hard-pressed for this; DPS in a C4 gas site is like 1/5 of that of a C5-exclusive gas site.
If the site you are planning on clearing is not one of the following: Exceptional, Infrequent, Isolated, Rarified, Uncommon, or Unusual Core Deposit, or Instrumental or Vital Core Reservoir, take the advice of the Paladin-users above.