bah on saves... your fort is fine. my build that as I mentioned is simular, I can add it if you wanna look (didn't do the two weapon feats cause it was too easy to get that from gear) but keep the damage immune feats, it is your niche'! my wm version has 98% on all phys and will be over 100% phys immune once she demi's and can wear an asmo item..,. she is tagged to cania so far and have saves of 60something fort 51 reflex 49 will and really festers ALOT and will lose her defensive weaves when he hits styx but that is only on a few different maps in hell. But with such awesome phys immunes and of course the DD crit immune she was tanking Belial last night (IE keeping him off the squishies) and hitting him for 200+ a crit to boot.
So saves are nice, but don't let them effect your overall 'niche' of your CC.