Guys,
i have made a great number of springs using 1095. Heat to 1450, quench in brine without stirring or swirling the part. Temper at 810. Please realize that the heat treating of steel will not effect the load/deflection property in any way - not at all. Identical shaped springs tempered at 650 or 750 or 850 will all have an identical load/deflection characteristic. The only way to make a spring stronger or weaker is to change its physical shape, size, or thickness.
Here is a quote from people who know:
The Iron Age Volume 89 May 9, 1912, page 1151
The stiffness of a piece of steel cannot be increased by alloying nor by heat treatment. By this I mean that provided the elastic limit is not exceeded, the amount of deflection for a given load cannot be decreased. However, heat treatment will raise the elastic limit so that a much greater load can be carried without causing a permanent set. Until the elastic limit is reached all steels, no matter how treated or of what nature, will deflect the same amount under the same load. However, the poorer grade steel or the un-heattreated one will reach its elastic limit first and will then deflect much more and retain a permanent set.
So, the answer to the first question is there would no difference at all between the three identical springs made from W1 O1, 6150.
Jim