Sorry this might be a stupid question, but I have found that some setups give the ball more dip and some setups give a different kind of spin. I think this is associated with dwell time. I notice when watching some college players and especially roger federer the ball just dips before the line...
Not to be a jerk but if there is that much of a difference on your serve with similair racquets, then thats your technique problems not the racquets problem. If your lack of hustling is the only reason you can't use the FXP Prestige MP then again I would just focus on getting your feet in...
Feel is very subjective, but the consensus is that softer strings generally provide more feel.
Personally I hate a mushy stringbed and prefer a more crisp feeling string.