+% Damage not affecting Elemental Damage is a bug which is scheduled to be fixed in the next patch though. It's true that the base damage on it is about as low as it gets. I'm in no position to say though if you'll get more damage out of rerolling the base damage or rerolling RRC into +% Damage. I suck at theorymath.
I've played around with Odyn Son all week-end, and I gotta say, it is (seems?) a far superior weapon to Won Khim Lau. The proc is simply too good to pass, in my opinion, even with an average roll (refer to the original post for the stats I'm comparing).
With my current gear, the proc hits for 4 to 8 million. On 3 targets, or 3 times on the same. It's almost ridiculous. It's essentially like having a new skill, free of spirit cost. Everything hits a tad harder with my WKL, but the bonus damage on CS, etc., simply can't make up for 3x extra 8 million hits.
Paper DPS went down nearly 100k, but I "feel" it went up 100k.
Considering all of your 3 weapons are well rolled (dexterity and socket), I'd go with Fulminator and Odyn Son.
Won Khim Lau does not bring much to the table besides a bonus to lightning damage, which OS also has. Fulm. and OS both have procs, although if I'm not mistaken only OS's will benefit from % lightning damage, which are better than your WLK's LoH. And both your Fulm. and OS have higher base damage than your WKL, so more damage overall.
In your situation, I wouldn't even hesitate and go with Fulm. + OS.
I've been rolling with a TF/WKL combo for quite some time and Odyn Son dropped just now. Reading around the threads here, I noticed OS's proc is one of the few to benefit from % lightning damage, and I'm wondering which weapon would be best for me. My concern is OS rolled with no socket and no dexterity, so I'd have to do without dexterity. Does the proc and higher base damage outweigh the lack of dexterity? If I switch to OS, should I reroll the vitality or the area damage?