If you work on CAD/CAM and 3D works, you need an Open GL optimized GPU.
Your can choose these below :
a. ELSA Synergy 2000 : NVidia Quadro2 EX, 32MB, AGP 2x/4x, [$ 165]
b. ELSA Synergy III : NVidia Quadro2 MXR, 32MB, AGP [$ 310]
c. ELSA Gloria II : NVidia Quadro GLInt, 32MB, AGP
d. ELSA Gloria DCC : NVidia Quadro DCC, 64MB, AGP 4x [$ 675]
e. ELSA Gloria III : NVidia Quadro2 Pro, 64MB, AGP 4x [$ 720]
f. ATI FireGL2 : 64MB, TV/DVI, 4x AGP [$ 749]
g. ATI FireGL3 : 128MB, DDR, AGP Pro [$ 1,355]
h. ATI FireGL4 : 128MB, DDR, Dual Monitor, AGP [$1,959]
I'm not promoting ELSA, but as far as I knew NVidia's Quadro GPU only sold to ELSA.
There is Matrox G series, but it's only 2D; you can't get good quality in 3D works.
And ATI has its own type GPU, the FireGL.
Your need is not a GeForce series, though a GeForce3 Ti550 can't show it's speed on "3D works" which is different with "3D games".
For an intermediate works, you can choose an ELSA Gloria DCC, not too expensive but good on CAD and 3DS as its driver optimized to those programs.