I used Kennametal’s 1.76 K-factor for that endmill with the cutting parameters shown in the workbook. The cutting parameters were chosen to minimize cutting forces while keeping within Kennametal’s calculated acceptable operating range for the endmill. Similar parameters for the 1/2" version of that endmill are shown here. If you compare predicted performance with the 1/4" endmill, you’ll see that the 1/2" endmill should further decrease cutting forces. (They should be cut in half at the same MRR). Chip clearance should be improved with the larger endmill too.
I’ve learned from @spargeltarzan and others that K-Factor is dependent on much more than the just workpiece material. Cutter geometry (rake angle, edge radius, helix angle, etc.,), chipload, and the use of lubricants can have a significant impact on it. So, calculators that consider those factors should provide much better estimates of milling performance. Kennametal’s probably does that, as does the “new kid on the block” Millalyzer.