Most of you won't be aware there is a rather interesting thread running at

http://www.ericbehme.de/phpBB2DAN/viewtopic.php?t=151

where Dan and Huehnerschaenders have been working on a 3d landscape engine with grassfield engine combined.

Using shaders Dan has improved thee perfomance of the engine 5 fold. Even if you aren't doing anything with DanJetX it is worth taking a look at their results.