In A Beast Cannot Feign (Gaia's Wasp Part 3) a Wyrm uses his boat exhaust as a weapon, destroying a ground target with a forty-gram, 0.3s burst of exhaust traveling two hundred kilometers per second.

How would that feel, for the pilot?

40g = 0.04Kg of exhaust at 200KPS  = 200000M/s carries momentum of 0.04Kg*200000M/s  = 8000KgM/s.

By conservation of momentum, the 900Kg boat would be accelerated forward by 8000KgM/s / 900Kg = 8.9M/s, or 20MPH over 0.3 seconds, a brief but exciting three-gravity shove.

How would that feel for the target?

The burst of exhaust would carry kinetic energy of E=MV2   = 0.04Kg  (2105M/S)2   = 1.6109KgM2/S2   = 1.6 Gigajoules, roughly the same energy as 350 Kg of TNT.