Primary vs extended partitions on Linux

Partitions don't really exist for the harddrive. They are just some structure the os uses. The os needs them to have different filesystems on one hd. The information that a partition consists of is basically startpos length. This information is cached by the os and given to its block device layer. When accessing the disk the starting offset of the partition is added to the block the filesystems wants to write to. Thats it.

Extended partitions have a small disadvantage during initialization. There is an additional reference that needs to be resolved which might cause one more io request. This should not be any problem.

No, you will have zero performance difference between a primary and extended partition if that is the only difference.

However, if the partitions are at different locations on disk, you will notice a difference for that reason.