That brings you to the engines themselves. While there are promising noises out of Avidyne regarding the next-generation systems, they aren't ready for implementation just yet. With that in mind you see two possibilities. The first is a single central drive, which with the boost from the main plasma injectors will perform at above-expected parameters and give the design the linear acceleration it needs to maneuver.
Alternatively you could mount a pair of engine clusters on port and starboard, which would push the spaceframe to its maximum tolerances. While a ship of this size will never maneuver like the Excalibur, it would provide enough thrust and attitude control to engage most heavy cruisers in the warbook with equal agility. It's not the worst capability to have, though you never know what the future holds. If the steady inflation in size holds true, the Federation will be punching up on the mass scale in the second half of her service life.
In any case, the choice is a binary one. If phasers will be the main source of damage for the ship, then a better-than-standard engine output is all it needs to engage both peer opponents and any smaller vessels during fleet actions. If you expect a torpedo ship or one-on-one engagements are the more likely outcome, then you may want to absorb the extra cost of the engines to maximise on-target time.