NEC based antenna modelers are available free and can be used for reliable simulations. The latest in 3D modeling 4NEC2, even allows you to model a WYSIWYG model by its user friendly interface and its free. You can find it in the link below, if you are also looking at modeling wire antennas then this is the software, you need look no further.
4NEC2 is a Method of Moments(MoM) solver just as the earlier Zeland version of IE3D(now with mentorgraphics) and you should therefore be expecting similar results.