I have done this test quite some time ago but never mentioned it here. My first intention of it was to prove fallowing statement which I did read in the forum: ,,upgrading a Nightblade into Acheron has no loss in damage since Acheron is so strong" (which proofed to be a total exaggerated lie).
For my test I did use full damage bonus the whole time. So all damage numbers are done with a damage bonus increase: Maximum! against the Gremlin punching bag of the T3 guild training hall.
The lower number indicates the 2nd hit (which is equal to the 1st hit) while the secound number indicates the 3rd hit of the 3-slash-combo of these swords.
Results:
Nightblade, heat 10: 363, 462
Acheron, heat 01: 299, 389
Acheron, heat 02: 305, 394
Acheron, heat 03: 313, 403
Acheron, heat 04: 320, 411
Acheron, heat 05: 332, 426
Acheron, heat 06: 349, 446
Acheron, heat 07: 366, 466 <- you can call this finally equal to nightblade, heat 10
Acheron, heat 08: 383, 486 (3rd hit is displayed as normal weakness vs gremlin)
Acheron, heat 09: 403, 509 (3rd hit is displayed as normal weakness vs gremlin)
Acheron, heat 10: 422, 532 (3rd hit is displayed as normal weakness vs gremlin)
Here the screenshot proofes:
Here a screenshot of the Damage bonus:
http://fs2.directupload.net/images/150630/uczpf4qa.png
Nightblade, heat 10:
http://fs1.directupload.net/images/150630/xb94bvxw.png
Acheron, heat 01:
http://fs2.directupload.net/images/150630/z9nkvfgk.png
http://fs2.directupload.net/images/150630/9cu4n96w.png
Acheron, heat 02:
http://fs1.directupload.net/images/150630/ruaais4h.png
http://fs1.directupload.net/images/150630/g9spjtzl.png
Acheron, heat 03:
http://fs2.directupload.net/images/150630/x3okohpk.png
http://fs1.directupload.net/images/150630/armo5c63.png
Acheron, heat 04:
http://fs1.directupload.net/images/150630/dx2t38wx.png
http://fs1.directupload.net/images/150630/ruvjhrgx.png
Acheron, heat 05:
http://www.directupload.net/file/d/4034/bzjq43va_png.htm
http://www.directupload.net/file/d/4034/h9z8w5d4_png.htm
Acheron, heat 06:
http://www.directupload.net/file/d/4034/ppwzapqz_png.htm
Acheron, heat 07:
http://www.directupload.net/file/d/4034/nemyvsl8_png.htm
Acheron, heat 08:
http://www.directupload.net/file/d/4034/6xjgdaek_png.htm
Acheron, heat 09:
http://www.directupload.net/file/d/4034/kseoukcq_png.htm
Acheron, heat 10:
http://www.directupload.net/file/d/4034/ryk4os87_png.htm
Now do it again at d28!