I found this "RejectThreshold" tweak last night, and had really great success.
I never could use the "No BufferPools" tweak, too many graphical artifacts.
Full post and thread is available here:The RejectThreshold is a cut-off. Calls from the CPU that are above this amount bypass the bufferpool and are sent straight to the GPU. With no bufferpool or threshold, all calls are sent directly to the GPU, which is the cause of instability. Anything below the threshold amount is sent to the bufferpool.
RejectThreshold=524288 //512Kb = 524288, 256Kb = 262144, 124Kb = 126976, 96Kb = 98304
I haven't tried this with the bufferpools yet, but just using it alone at 262144 (256k) setting, I am having very good result in PNW, where I have usually seen a slight dip in fps.You can still specify a bufferpool size, I use PoolSize=2097152 to set a 2MB pool. Also, start with 512Kb for the RejectThreshold, and increment in steps until you get graphic glitches or a crash, than raise it back up one level. I am at 256Kb right now, I am going to lower it to 124Kb soon. Do not go below 96Kb, at that point it is better to just set the PoolSize to 0, but this is unstable for many people, unless you have an ATI 5870, which is nearly impossible to crash in FSX.