Copied from EU forums, credit goes to Zetsuro. I agree with this post and you guys should know this too.

Hey guys, I am just letting you know that it will NOT kill your stats if you decide to use a daikatana. In fact, it may be better in the end.

Okay, so, this is just based off of straight numbers, no bias in any ways. I have just heard that using a daikatana is detrimental to a WA's attack which is far from the truth.

First, we'll take a Mith GS+9 and a Mith DAI+9,
(after +7 i believe it does not require any more points to use a gs or dai of a higher grade; GS and DAI+9 have same stat requirements for GS and DAI+15 for example.)

Next, look at the stats to use each.
The GS needs 612 STR, 68 INT and 68 DEX
The Dai needs 476 STR, 68 INT and 204 DEX

For a WA, a point in STR = 0.30 ATTACK, while a point in DEX = 0.20 ATTACK. INT = 0 so we don't count it.
Some simple calculations;

GREATSWORD:
612x0.30 = 183.6 ATTACK
68x0.20 = 13.6 ATTACK
+3 ATTACK for being a GS
Total = 200.2 ATTACK - rounded to 200 attack

DAIKATANA:
476x0.30 = 142.8 ATTACK
204x0.20 = 40.8 ATTACK
Total = 182.8 - rounded to 183 attack

As you can see, we find that the so called blasphemy to the WA class, the Daikatana, holds it own and only has 17 less attack than the Greatsword.

However, we all know that Daikatanas are much cheaper when it comes to price. I got myself a 52dmg Mith Dai (haven't +'d yet) for only 500kk (I PLAY FROM NA), while a GS of that sort would cost upwards of 1 Bil, if there were any even on the AH.

With the extra cash I'd save from buying a Dai instead of a GS, I could improve my other parts which would consequently be more effective than the 17 lost attack.

TL;DR - The GS only holds about 17 more attack than the DAI at the mithril grade. Give or take a few attack, the Dai costs much less and therefore it can be on par if not better in the end.

Thanks for reading...happy hunting :P