"Accurate" would depend on the context. The lifesize prop used in ST4:TVH would indicate a very small vessel, perhaps just 50 meters in length. Comparisons of the photographic model against other photographic models give sizes ranging from 80 meters to several hundreds of meters. Comparisons of the photographic model against real backgrounds, theoretically available from ST4, are inconclusive, but the rough 130 m length is suggested in the matte work of that movie, and of ST3; the prop, only properly seen in the final sinking scene, might have to be disregarded.
Also, the comparisons in space shots might be taken to indicate the existence of two different sizes of craft, plus an optical illusion that is perhaps related to the presence of a cloaking device aboard these ships. Perhaps the cloak comes with a "cat in a corner" mode, and regularly makes the ships look slightly larger than they really are? Or perhaps this is a common involuntary side effect or malfunction in the cloak?
If we drop the cloak theory, we probably have to believe that Klingons build at least a dozen differently sized but identically shaped variants of the design...
Timo Saloniemi