You really need to be more specific. IT really depends on the game and the engine. Some of the guys working on the standoff mod might be able to tell you the uper limits of the vision engine used for prophecy and secret ops but it won't be the same as the poly count for wc3/4. And priv, wc1,2 used sprites in game that were pre rendered from some antique model format.
Hehehe I used the new post button so I didn't notice that you were most likely asking about the Gemini Gold ships. In which case John or someone else familiar with the vega strike engine and its next iteration might be able to comment on the poly limits per ship and how it affects framerates and such. Engines can be capable of higher rates but practicaly are unplayable on current systems that way because it becomes a slide show. But I imagine someone on the team can comment on that, though it's going to be higher for capships than fighters.
I know that when I was modeling stuff for WCU/GG/Whatever, the counts varied from between under 3k tris up to around 8k tris or so. Just depended on the ship and how complex I was looking to make the model.