I noticed funny thing, first with Titans, now with Dragons.

More powerful variety of Titans and Dragons drop less gold than less powerful. According to extracted game data, Gold Dragons should drop 400d10 Gold, which should average at 2200 Gold per Dragon. You get 700-850 Gold instead. It feels as if game substracts 1600 Gold if it overflows that value. Strangely enough, i can remember dragons dropping 2k gold in original version.

Titan drops 200d10 Gold, 1100 on average, works as it should.
Noble Titan should drop 300d10 Gold, 1650 on average, but he drops around 200-300 Gold instead.

Was that changed in some official patch or Grayface patch? As from other things I remember, unpatched version (1.0) also had different price tables for training - getting gold to train at Lv.90ish was nightmare, as it required dozens of thousands of gold. Now I am closing to 80 with million of gold already and training costed me only 5058 Gold from Lv.77 to 78 per char. It was like 10 times more expensive in unpatched version (it was following World of Xeen training cost formula iirc).

Hey! I remember the thing with the high amount of gold needed for the training :D It also fuzzed up the game in the mid-levels because you had to invest all your money for the level ups.

For the drops of the monsters, i am not actually sure if the unofficial patch fixes it. Nontheless i would recommend to install them, as they fix some bugs with quests as well(at least i remember it for MM7).

Fact for fun, years ago I hacked my characters to see how far they could train. With maxed Merchant skill they could train only to level 715, then training cost would overflow into negative, causing very weird issues and calculations. With new training costs you can actually train well into thousands of Levels, given enough time. Those patches are already applied to GOG version. I simply wonder what patch changed this as well as training costs, because I clearly remember looting 2k per Dragon.

I'm pretty sure they're not, at least not the newer ones.
There are still bugs with scrolls not allowing to choose their target, making"Stone to flesh" and "Raise dead" scrolls unusable. Grayface patch AFAIK fix this.
I've newest version of MM6 reinstalled from gog galaxy.

I think newer versions of patch aren't installed because they don't fix any major bugs but alter the game significantly (adding mouselook and such).

I know that GrayFace patch is in, because it fixed locked doors in Shadow Guild, added mp3 audio instead of CD tracks, AlwaysRun (as in MM7+), no flip on exiting from buildings (as in MM7+) and such.

Yes, now that I think about it that may be the case. I remember I was initaily confused that no "flipping" occured after leaving a building, which was pretty annoying "feature" in my original disc version.

Are dual-wielding formulas also fixed from Grayface patch or are they still the same as in unmodified game?

Depends what you mean. "+Attack" and "Damage" add up. ABout double recovery time I am not sure, but it feels like working as I don't notice any significant delay with my dual-dagger character. Newer Grayface patch is adding visible Recovery Time stat, but in unaltered game this stat is hidden.

However, I have noticed interesting thing. If weapon has additional bonus damage (e.g., of The Dragon), then this damage will ignore resistances AND immunities. So you can use weapons of the Dragon and deal full damage to Fire Elementals (90+ damage from Ares, so sweet, and that's with very low Mace skill).

I was thinking about "double recovery". I also cannot say whether or not it is applied :)