Q: i have the current Mac Pro the entry level with the default specification and i feel some slow performance when applying after effects on my videos using final cut pro and also rendering a video takes long time ? what upgrades do you guys suggest?

This includes various configurations and performance of the 2103 Mac Pro. It may help explain the "poor" performance.

http://macperformanceguide.com/topics/topic-MacPro.html

Most important is to keep all your video media on a fast external Thunderbolt or 4 RAID HD with thunderbolt connection. And probably more RAM 16 GB is good

Start by check performance of your computer with Activity Monitor:

OS X Mavericks: About Activity Monitor

excessive Red memory pressure means you need more real RAM.

256GB SSD  it shipped with will run low and one of the things to watch.

Default memory is 12GB  also something to think about.

D500 and FCP-X 10.1+

http://macperformanceguide.com/index_topics.html#MacPro2013Performance

Five models of 2013 Mac Pro running Resolve, FCPX, After Effects, Photoshop, and Aperture