Shun does not crit, but I really wish it did. Therefore Critdmg/rate means jack for this ws.
Fire offhand is pretty much the best offhand you can get outside of abyssea period. Kamome is still best inside(I think?). Its definitely worth upgrading since you have Kikoku/Kannagi.
Here is what I use:
http://www.ffxiah.com/item-sets/267299
As you can see there are a few alternatives that could/would be better such as replacing Demonry for Bomb core(Maybe?), or maybe epona's ring over Rajas ring? Some advice on this from anyone would really be Appreciated as well. ^^
Hope this helped somewhat~