Another issue with working on small screens with fairly high poly count models is that you may end up not actually rasterizing much screen space ... so your polygon setup code can actually be more of a bottleneck than your rasterizer i.e. seting up 120 poly is more expensize than blitting 100 pixels.
But if you reduce your models too much they look shite when up close, LOD is not an ideal on low memory devices either.
This is an issue that I found when writing a commercial rasterizer a while ago, significant speed ups can be produced by extra careful handling of poly/strip/fan data and poly reduction prior to setup..especially if doing expensive lighting.
Jim.