Very well yah! Setting the port timing flush favour the engines ability to make peak power. It will soften the lower rev range some though. Correcting the squish will gives gains across the board, and running a decent amount of compression will also give good snap down low.
Have a look at these sims that Dmcca ran on the 300 he worked on.
http://www.gasgasrider.org/forum/sho...8&postcount=69
You can clearly see what happens to top end if you go too far without other porting mods. On the 300 I always ran the stack flush as it still had heaps of power down low and I prefered the softer delivery and more top end. On the 250 I actually set the piston above the ports a bit, however this was using a race ported cylinder so it had already been set to favour top end over bottom. The port timing just brought it back closer to stock config.