HELP! sgi 3000 or 4D ?

[Charles L Ditzel]

HELP! 

As a possible newcomer to the sgi world i need help with
the following question.

How portable is code written for 3000 series SGI
machines with the 4D series?  Two types of software
come to mind : mex-oriented software and those programs
that do not use mex but instead use the graphics primitives
library.

We are about to purchase an sgi machine which *must*
run 3000-based (internally-produced) programs...one of 
the decisions to be made is : if it is easily ported to the 
the 4D then we will go with a 4D. if not then we will
go with a 3000 series.  Any helpful opinions gladly received!

(obviously if i had my way we would just get a 4D..but
reality may be getting in the way :-)