Great discussion guys.
I think that from the outside, I can see your discussion being a simple misunderstanding. In my mind, you are both right, but you are talking about different types of responsiveness.
Rod is talking about responsiveness in regards to power transmission and killclimbz is talking about responsiveness in regards to transmission of position. Right?
In other words, Rod likes a binding to be stiff and transmit power straight to the board. To him this means responsiveness.
Killclimbz on the other hand wants the board to react to minute positition changes and inputs that he makes quickly, so he needs a binding that allows his ankle to flex more freely and quickly while the binding still gives the needed support.
To me, it is a discussion similar to the function of bicycle shift cables vs. bicycle brake cables. One transmits position and one transmits power. Both are responsive. Both also transmit the opposite function as well, but not with the same responsiveness.
Please, let me know if I am way off.
Here is my take on the situation. Most softbooters, especially park riders, want to transmit position much more than power. Most hardbooters want to transmit power more than position.
If you are in the power camp, hardboots are the most responsive thing you can ride. If you are in the position camp, softies are more responsive.
When talking about step ins, a lot of them tend to transmit more power and less position.
By Rod's definition of "responsive", step ins are moreso.
By killclimbz's def. of "resp." step ins are not.
In the end, a good rider will be able to transmit power and position regardless of what he/she is on. There are hardbooters who can rip the park, pipe, and BC on a race board if they want to and there are softbooters who can win races and carve like crazy. At our annual hardbooter event, a softbooter won the circle carve in the expert class two years ago!
This has all been a major threadjack, so let me get back to the OP:
If you liked the burton step ins, you may be one who considers the term "responsive" to mean good power transmission. If that is the case, either pick up one of the later model Burton SI's (which transmit power very well and do not loosen up the way yours did) or pick up a stiffer model of Flow bindings (which also transmit power very well). If you are looking for something with a little more versatility in the park but still want to step in, check out Flow's freestyle stuff (which transmits position a little better than their freeride stuff)