2.If you set SF8=0 you will block all 384K rab, so you wont allow high throuput data on R99 and save most power. SO no mobile can have SF=8
However you can have SF 16,32 set to non zero values to allow data on the mobile that have only R99 Capablity.
I have tried blocking SF8=0 and SF16 =8 and SF32=32 and it worked fine and power rejection went down on the voice side. Try it
Howerver the basic assuption for all above setting is that you have HSDPA on so you can afford to minimize the R99 traffic
4. Turn on GSM direct retry :If you hit with power congestion on UMTS you can turn on the Direct retry to GSM to provide relief on UMTS .
Make sure you define the target GSM cell for retry .Generally the target cell is the cosite GSM sector .
Also make sure that you enough capacity of GSM to handle the additonal traffic