allways use spatial fine, everything else will fail on you miserably.
Ans yes you can pus that tesselation to infinity.... Ist sjut that it may seem to stop a t a edge coefficeint of 0.999 but in truuth you can easily push it higer than that. Baceuse the edge factor is based on physical size so you can scale the thing up freeze then scale down and not freeze to pump it further.
JUST make sure your gloabl accuracy is set to highe enough for the import otherwise there IS a gap between patches. As you might udnerstand 3d modelling packages dont uysualy do over shell tesselation lieke cad applications do. Thats becasue theres s philosophical divide betewwn their makers.
note theres no easy andswwers here,i usualy export objs form proe and adjust teh teselation in proe, UNLESS i use renderman in wich case i dont care as it eats nurbs patches much faster anyway. Yes its simple but ist a demo, i havent got time to modeell a gareingene you know 
anyweay heres a sample importted form proe and rendered with teh fine tessaletion heres a picture (click to zoom its pretty big because of quality)
400) {this.resized=true; this.width=400; this.alt='Click here to open new window';}" onmouseover="if(this.resized) this.style.cursor='hand';" onclick="if(this.resized) {window.open('http://www.hut.fi/~joojala2/highend/tesselation.png');}" />
legend left to right original view res, res after pressin 3, tesselation shown, render in maya with the smooth edge turned to 0.99, look maa no creases but 0.98 is way too high i coul probably do with 0.8. then theres the one done with spatial fine, on the surface AND the trim! rewnders in 0.8 seconds on just one proc.
you can se a slight artifact in teh mr render wich is brought by too small tolerance isn the exportter settings , so i d need to reimport it better.
NOTE allways make view dependent spatial fines. otherwise it defeats the purpose.
Understanding tesselation is teh key to succes on the cad rendering arena 
Anyway you may want to bias your raytrace a bit since it can easily pick certain bad artifavcts even with right tesselation. but fro scanline peatches.
