[1.2.361] Level 140 Items

Um... learn to math?

Let's say you have 1000 (for easier mathz) base of your primary statl.
Now let's say you reset 166 into your secondary stat just to equip these. That would put you at 834 STR or 83.4% of your original STR (you lost 16.6%).
We'll pretend that Dex is totally moot (which it isn't) which means that, due to the purely multiplicative nature of the damage formula, you lost 16.6% of your damage.

Now let's say you somehow have 200 w.att from all your equipment. We'll ignore the extra attack that the equips give and focus only on the set bonus, so we'll pretend that these have the same stats as your old stuff.
45/200 = 0.225. You're getting 22.5% stronger purely from the set bonus.

Now to throw these into the actual damage formula. Since you're a Dark Knight, I'll use the spear/polearm multiplier.
Pure STR
1.49 * 4 * 1000 * 200 / 100 = 11920

140 Equipper
1.49 * 4 * 834 * 245 / 100 = 12178

Overall, you're getting a 2.165% boost.
Again, this is making a couple of assumptions in favor of the dexless route.
It's assuming you have no equipment that gives Dex and that you have 200 W.Att.

Couple of things for your fucked up math to realize.
1. Holy crap, a 2.65% buff for something that is right now, by the looks of it, impossible to get. MY GOD. WHAT AN INCREASE. I MUST PUMP 166 STATS TO GET A 2.65% INCREASE USING YOUR ASSUNED NUMBERS.
2. Your weapon attack is too low to even be considered.
3. Dear God, the damage formula doesn't follow BASE stat, it follows TOTAL stat.
4. WHERE'S THE DEX IN THE FORMULA?

If you're going to prove me wrong by using your illogical numbers, at least try to do it right next time.