My backup Tomb Raider Anniversary had some lagging problem while playing FMV. Tried dumping the image so many times already. It turn out that my 4GB Memory Stick Pro Duo was a fake after checking in information>unknown. After google a bit I found that after changing the file format from FAT32 to FAT16 will solve the problem. It will speed up your file loading dramatically and the FMV/game lagging problem solve.

From windows:
Run cmd,
In DOS prompt type in following
format e:/ fs:FAT
e:/ is your ms drive.

yeh its wierd, PSP's seem to prefer fat16, yet the PSP formatter always uses FAT32 :/

I did mine to FAT16 the other day on my 4gb sandisk pro duo gamer edition, did a speedtest on it with the tool called BLACKspeed and it was a bit quicker, but it generally feels roughly the same.