Make a new Imperial supergun. Call it the Pwneratus Imperator. Sounds like about what you are looking for.
Actually, we are thinkering about that

Big lines of what we came up with, not playtested, not finished yet either.
- The nova cannon is a heavy long range artillerypiece using the normal guntable. One additional right column shift for firing over 60 cm.
- Make it an equivalent of FP6, roll to hit as normal, a hit doing D6 damage, shields 'absorbs' damage as normal. The multiple hits indicating its accuracy is better at short ranges but only one D6 is rolled for damage.
- no min range.
It's also possible we ditch the concept.