wood arrow spine

[Jim Wright]

I'd like to hear some thoughts concerning what the rate of spine change should be when going up (or down) in point weight on wooden arrows. For example if you shot a 50lb @29" Hill style longbow with 50-54 lb. spine, 30" long, 125 gr. point arrows, total weight 550 grs. and you wanted to go up to 175 or even 225 grain points keeping  total weight the same, how much stiffer spined shafts would you need?
 Common wisdom seems to be 5 pound spine change for each 25 grains of point weight change but Im beginning to wonder.