@ Arctic Circle: You are right. Even at Epic Sidar are about 1-2 difficulties easier (In Marathon its completely riddiculous but that takes to long for FFH2 anyways imo. And i do like long games. But FFH2 takes care of that without tempering with gamespeed already.).
Not least because their more or less best way to research is straight for Warmongering (rush military strategy after mysticism if you find copper near at mining. Then go KotE for Enchanted Blade) which is much more potent in slower gamespeeds.
But they are allready "balanced" somewhat on paper by the different value of the yields (1

7

is worth much more in quick than in marathon.).
But that doesn't really translate into a real parity due to a maximum number of units gained per Turn = 1 so you proportionally get up to 4 Times as many Warriors / Scouts built at Marathon in comparison to normal or 8! Times as many as in Quick. Which more or less directly translates into shades gained. Also the critical time to get the first 3-5 Shades gets to be proportionally much later.
Also if given the choice of 1 Shade in quick or 4 in Epic (more or less the same balanced yield on paper) i whould take 4 in Epic any day of the week because of the ability to customize and spread out. (all 4 Choices are decent.)
Sidar are only really fully playable / balanced at normal speed (and they are a rather powerful civ at that speed + my favorite civ.) at slower they are to powerful to be balanced (since there is no difficulty above deity their is no constant challenge possible in all games the way the AI is now + the harder you are pushed, the stronger you get. But sure that will change soon enough.) at quick they become a rather weak civ since all their strong points suffer and their traits are weak for that gamespeed.
(Problem with adding one Level for each gamespeed for Shading and Starting at 5 at Quick / 6 normal / 7 Epic / 8 Marathon whould be that free XP can be made available out of the box. That again whould make it to easy to get shades at quick just to get it balanced for epic. And at Marathon the curve might be to steep + the half-xp option is there for a reason.
Thats enough of a fix which can be done and is highly reccomended if you want any challenge from the game while playing sidar at marathon.)
So if you play slower just enable half-xp from combats. Should fix the thing allright.
FFH 2 is balanced for nomal speed (qoute from Kael / FFH 2-Team)