The small 58cc head will typically raise the CR by 1.3 to 1.4 points vs the 72cc head. Since they vary you really have to cc each head to compare.
As discussed/debated often here, the small head responds better on bigger engines if it also has bigger valves AND is unshrouded, which will add a few to that 58cc.
For some numbers, I went into the Gonkulator and swapped a stock 194 head onto a bone stock 250/155hp. The Gonkulator picked up 3 ftlb and 6hp ; the little head gives higher CR but is otherwise not quite as good. That's the best I can MODEL the head. For actual differences you'd just have to try it or read the many threads on this topic here!
