Perhaps not. A height field is one primitive that's easy to highly
optimize. There are numerous PC games using height fields that run
reasonably fast on a 486. Instead of transforming every vertex and
rendering those 80k triangles, (I think) they use a floating horizon
algorithm. Each covered pixel requires a small O(1) amount of work
and is touched exactly once, plus O(n*m) work for an nxn grid and
m sample directions. The results are quite impressive.
Of course, waiting for 40k heights over a 14.4 modem might try the
patience of those PC gamers.
Cheers,
-chris