Flashing only rootfs leaves stuff in n900. Also restoring same apps that you had before flashing is not either helping to pinpoint problem source. To see if it is really slow then do following -Backup and copy backup to desktop pc or micro sd -flash emmc and rootfs -restore only contacts and conversations -use it. is it slow? -if so then try overclocked kernel -use it. is it slow? AND NOW you can install apps/widgets and experiment if it starts to get slow.