Here is Chris Wang's dyno showing about 3 HP gain across the rev range going from a single Extrude Honed 1998 SVT upper to a dual Honed 00 SVT upper + 00 SVT 34mm lower.
http://www.contour.org/cgi-ubb/ultimatebb.cgi?ubb=get_topic&f=47&t=000056&p= So, a non SVT using the dual Honed SVT upper & lower would probably gain more. Maybe 5-6 HP? Probably more power available if the secondary butterflies were optimized or perhaps removed. Of note, I think your Leo Capaldi has gotten up to 320 + HP using a more extensively Extruded Honed intake. Mirko had 260 HP with the upper as well. So, maybe given enough Extrude Honing to match head port sizes its not that restrictive... Just my guess.
