That will depend on the rules used. See thtat with HG (or MT) rules, once again due to most ships being misión killed but not really destroyed, unless the varg hordes are strong enough to overcome the SDB fleet at once, they will fight again the whole fleet (or nearly so) next time, as, if the system has any repair capacity, most of the SDBs will be repaired in a few weeks (and any ship left behind by the Vargr will be reparied and added to the planetary fleet also in a short time).
I guess you mean those in Rebellion sourcebook. see that the Aek-Naz Battlecruiser is fully ilegal according MT rules, as it has j4 at TL 11 (when TL 13 is needed to achieve it).
Also, in both cases, with Computer 5, agility 0 and armor 45-50 they will be soon dead in a battle against any Imperial ship.
To keep with the same book (and using MT rules), a single SEH light cruiser can make short of quite a number of them, with its 4 level computer advantage, lasers/sand enough to keep vargr missiles from hitting (even some lasers could be used offensively) and its J meson gun, that will take one ship per turn (without agility and with the computer advantage, they'll hit and penetrate config 35 out of 36 times, while the vargr factor 7 missiles will hit on a 9+ and need also 9+ to penetrate SEH's beams, and their D spinal PAs will hit only on a 8+)
Unless you have many more ships tan they have meson sites, your ships will be dead after a single round or two of bombing, and, in any case, with those cruisers, your losseswill be far beyond what is acceptable).