allmost - 2 SNs are - i believe around 120.000 damage to the shield ( out of the 140.000 it can take )
anyway - trust igiss in knowing about the overpoweredness of a twin SN. besides - having 4 tubes and a normal ( large ) powerplant is good enough. makes a very flexible bomber indeed. - with 1 SN, 2 nova and 1 train CD, its the dream of all pilots.
you can point damage ( SN ) any capital ship, you can strip them of their equipment ( twin nova ) and CD them. - a bomberpilot would give his both legs for such flexibility and power. - twin SNs is not everything. and 4 tubes with a normal powerplant are great as they are... and wouldn t unbalance everything.