Since I am on the absurd topic beam FC tracking speed maxes out at 100,000 so the latter example would be impervious to anything sporting beam FC.
Not necessarily, top speed is capped, the chance to hit something going 300,000 kms with even the most basic beam fire control and laser (although 4x range and 4x tracking speed so 5kms TS) still has an accuracy of 1% at 30k, so 100 beam weapons still have a 1% chance to hit, and this is basic tech, get more advanced and your still going to be able to hit very fast things much more easily, although range is still an issue but you can't really have an invincible ship at any level, you can still have an incredibly hard to kill ship (whether by speed, shields or armour) but it can still be hit and can still die.