So currently, the character I mainly grind with is a Striker... I don't PVP much (occassional node war or guild war). Right now, he's equipped with a Nouver vambrace, but I'm thinking since I mainly fight the monsters I should switch to the Kutum (it does have more monster AP). So, would it be a good idea to switch it over? The comparison is below. I really think the extra monster ap and accuracy will help me out with the higher end mobs versus what the nouver vambrace has been doing.

Also, the other question I had was, if I do the "exchange boss gear" quest through Jetina and I've already got a Garmoth's heart and Caphras on the weapon, will it automatically change from Fiery Nouver to Fiery Kutum with the same caphras? Or do I need to remove all of that before I perform the quest?

You definetly will do better with Kutum in PvE. So yes - replace the nouver with Kutum whenever possible.

And I believe you'll have to exchange boss gear without anything else in it (Extract caphras, hearts e.t.c. before exchanging). No. Personally I've never tried it myself, but if anybody did feel free to correct me here.

Well, it doesn't look like I can exchange it. I pulled the caphras and the heart but there's no option for it coming the NPC Yisar. I suppose maybe because it was upgraded to PEN? I don't know. This is definitely sub-weapon made from the Jetina questline cause it's indicated in the weapon's description and it is unsellable. I just figured I'd try since there was the extract caphras event going on and it would cost me pretty much nothing.

You cannot exchange the Nouver for Kutum once it has been reformed, so sadly , you will have to outright buy a PEN Kutum instead. It will still be worth it due to the monster AP though. 

Thanks! I finally figured it out last night after doing some more thorough reading of a guide. Thankfully, I had already bought a pen kutum for my woosa (that I just use for boss trains)... and I have plenty of sub weapon exchange coupons... so I just switched them. It ended up not being as big of a deal as I thought it'd be. :)

Those exchange coupons come in  handy.

It looks like the only advice you really need is Advice of Valks :))

The wierd thing is at.. maybe at some classes and some brackets..but nouver is better... sometimes... BDO is wierd :D

Nouver is better in PvP for classes that go for glass cannon builds, which isnt many any more post this update, or some of the tanky classes using very specialised builds (eg with DR accs to get some more AP). 

In PvE, Nouver is better from the brackets (With Nouver) 261-272. However, these are brackets that many new players immediately cross after ending seasons (Since kutum is better again after reaching 261AP with kutum), especially now with the free pen BS and tet BS. 

Basically, unless you plan on doing PvP with special classes or special gear (In which case you really dont need my generalised advice here lol), get a kutum for PvE. The times when nouver was a good choice for PvE has long since passed with all the free gear we get.