If the feeds and speeds calculator you are alluding to is the one put out by Eldar over at HSM Advisor then I really don't have any info I can offer. If it's not then, perhaps HSM Advisor can give you an additional source of data to work with.
I have a 770 mill and according to the power curve that's generated for my mill, I get the most torque at about 4000 rpm. There appears to be an overlap of this same rpm/torque range regardless if I'm running the smaller pulley or the larger pulley. Since I like to go fast as opposed to going slow and strong, I try to set my feeds and speed around the speed side of the equation; although, I have generated feeds and speeds with my various cutting tools centered around maximum torque as apposed to maximum speed. I used the maximum torque settings when I was cutting 303 stainless.
The irony here is that with maximum torque I can take deeper cuts but at a slower feed rate. When running with maximum feed rates I'm taking shallower cuts so the time it takes to complete the same tool paths using one or the other of these two feeds and speeds calculations generally isn't to much different in terms of the time it takes to complete a tool path to a finished part or parts but, I use cheaper cutting tools. If a guy is using higher end cutting tools perhaps the benefits of custom profiles with optimum speeds and feeds would then be of greater benefit.
MetalShavings