some questions about my Molten Strike Marauder

I've been enjoying playing my marauder in the rampage league. I'm up to level 90 now and for the past 20 levels I've been using Kongor's Undying Rage.

Here is my build.

http://www.pathofexile.com/passive-skill-tree/AAAAAgEAAdwLYRLhFFIU9hkuGj4b-iE0IVUiryXfJy8n7SkuLPsxnjH7Mgk0jjWSNro4UzkOOuE9_EE_RmlHfkrITeNQVFHmVAtUSVcNWD1YY1ivXz9gxGEhZU1r2WwWbEZuaW6XbqpybHKpdud4DXloe4x8uH_jgSuE2YY7hxmHKYdqjM-QbJHOlIeZK5tYnsWkGaSsplepbqlzqZSsqrQvtfK8n72Bvoq-p8APwQTG2NIh0k3Yvdlh3D3d49-y45_kUel87w7xrPIv8kXynPZI9zL3vvxL_gr-j__T

I've done some strange things I suppose. I built an armor build when apparently armor is terrible. I don't use conc effect. I didn't bother even going to iron grip. I sort of just considered the fireballs from molten strike to be additional aoe and built straight phys.

I like my clear speed and my survivability isn't too bad (at least for soft core!)

My question is this though - Just how good IS kongor's undying rage. No one is selling it 6l. Is it worth 6-linking it or would I be wasting my fusings? If I did 6l I'd probably buy one that had a slightly better roll for just a few chaos. I just don't know if it would be worth it. I don't see a lot of rare mauls out there with the high end dps that kongor's has without being terribly expensive for me (like 4 ex+).

I don't really trade much at all so I don't have a lot to spend. I've amassed 1/3rd of the fusings I'd need to 6l. I just don't know how I feel about it or how much it is worth it.

Anyone else feel like sharing their molten striker? I'm curious how other people feel about the skill in general. Is it unusual to build it the way I have?

One question though, how does your Kongor hold up at level 90? is it still desirable in terms of damage, also, for how much did you get it ?

The one I'm using I got out of a box fairly early on. I was able to buy a new one yesterday with slightly better rolls for 4c.

I'm not unhappy with the damage at lvl 90. I can clear a 78 map at a decent speed. That being said, the majority of my nodes have been pushed into damage.