As I recall, the Realism Mod ups the attack rating of ships by 50%, also lowering their defence rating by 50%. This apparently increases the likelyhood of ships actually being sunk, removing the frustration we otherwise can get.

I still play with my ships unmodded, but what I do is instead of a single big stack, I use a number of small-mid stacks that are closely coordinated. I try to surround the target enemy stack, at the very least minimizing its escape routes, by placing my stacks in the target's zone of control, then I send my final stack - preferably the one with the admiral - to do the actual attack. The surrounding stacks get counted as reinforcements, giving me the combat strength I need to win, plus by blocking/limiting the target's escape I increase my chances of an immediate kill or allow for a quick follow-up attack.