Here is my two cents. I have only been into three rail for nearly 3 years and I am a recovering engineer (over analyze everything). I am also stuck with 031. So after convincing myself that I can live with semi-scale I can emphatically state the following. GO SCALE!!!!! You have the radius to support nearly everything. If you stay with scale everything looks right when coupled together. Semi-scale is very flexible in size. Somethings look great together others don't. Also, if you run passenger cars you will find that many 60 foot passenger cars are scale in width and height only shortened for going around 031 (for that matter many "scale" passenger cars are a 70 foot compressed length). Coupled with a semi-scale K-4 the locomotive looks too small. I am sure the SP semi-scale GS-4 would also look small. in my humble opinion you cannot go wrong with scale and do not obsess over the increased price because with the increased price you get a much more authentically detailed locomotive.
