Set the “Slow” Speed Control setting to “Fast”
Next you will want reverse the direction of controller application. This is necessitated because MW is a minimum-to-maximum controller, 0-127; so by setting the Speed Control to “Fast” (maximum), you’ll need a controller that can reduce values. Reverse the MW so that it reduces values as you raise it. This can be easily done setting the CONTROL ASSIGN screen so that RATIO parameter is set negative application.

Slow = all values between 0-63
Fast = all values between 64-127

By setting the parameter as you want when you recall this Performance, guarantees the Speed is as you desire, initially.
The MW will be set to apply negative values as you move it away from you.
The MW defaults to being in the down position... this will now be “Fast” and you’ll subtract values as the MW is moved upward.

Step-by-step
If you are looking at the Speed Control parameter... set it to “Fast”
While the highlight is on the word “Fast”, press the glowing [CONTROL ASSIGN] button
It will ask you to select a controller...
Move the MOD WHEEL
you will be taken directly to the Assignment.
Change Ratio from + value, to the same value as a negative value
You can see how this reverses the direction of MW application.
Press [STORE] to create a USER PERFORMANCE

Extra Credit:
If the CURVE = Standard
POLARITY = Uni
When RATIO = +32 this means the Speed Control switch occurs 1/2 way in the movement of the wheel. The higher the number, the earlier in the movement of MW the Speed change begins.

Even more options:

Note that the programmed setting for rotary Speed Control does not, alone, set the default speed for the rotary speaker. It's a combination of the programmed setting plus the value of your curve at the far left-hand side. If you think of the curve as having x and y values where "x" is left and right and "y" is up and down - then the far left is x=0 (x is equal to zero). This x=0 "y" value (height) is added to the programmed value as the resulting default value (when you load your Performance). Ramps (standard curve type) will always have x=0's y value (height) as 0. So if your curve is a ramp - then the programmed value will indeed always be the default value. However, there are curve types which allow for x=0 to have a non-zero "y" value. This would allow for you to have the default value as something different than the programmed value.

Default rotary speed sound when loading Performance: Fast. Modwheel in "close" position = fast, "far" position = slow.
You can set the programmed value to "slow" then under Mod/Control -> Control Assign set your curve type to Square with param 1 = 0, param 2 = 5. Ratio +49 (as an example). This doesn't gain you much - since it's the same type of result as doing this other ways -- but just demonstrates you can have the default as an OFFSET value - something different than the programmed value.

Thanks for your help!