Ok, I spent some time playing with some numbers and found out some interesting stuff (What? You don't find numbers interesting? Freak...). Since people (most importantly, Valk) seem to want training/arcane XP to move on to a flat rate system, I thought I would play with the numbers to see if I could make one work. What follows are the distilled conclusions from all my number tweaking and how I came to those conclusions. If anyone wants it, I can upload the spreadsheet I used for all this, but it's a bit more complicated/cumbersome than the first one.
Notice: All these turns are for normal speed. Gamespeed will affect these turns.
First: Arcane XP
I first found the # of turns to upgrade a 0 XP adept to a mage and archmage using the current system and taking into account taking the Channeling 2 promo when he hits mage and I even started the adept with one spell promo for the extra XP gain and assumed he didn't take any others. I did this for a plain adept, one with potency, one with mages guild, and one with both. I then found flat XP gain rates which gave comparable turns. I removed any XP gain from the spell spheres, since I think that won't be necessary in this system since it was sort of tacked onto the old one. The results are:
These are the best rates I found to match up the mage times, but the archmage times are a bit less. I thought about this and I think this works perfectly. The reason is that people were wanting non-combat and non-summon spells to give XP, but I think this simplifies it by just giving them a little bit more XP per turn. To balance everything out, the summon XP may need to be removed to prevent those casters from gaining too much XP, but that will be something to think about.
Another feature(?) of this system is how it interacts with XP gain on training compared to before. Presently, if an adept gains 2 XP on training (from apprenticeship, for example) it only saves you about 4 or 5 turns of waiting till it hits mage. Now it will save you about 20 turns (for plain) to around 13 with potency of waiting around, which seems to work with the slightly longer mage times. This may or may not be good depending on the wanted end result.
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Second: Training XP
I did something similar to arcane XP for this. I found the # of turns to gain certain lvls from 0 XP.
I couldn't settle on one fixed rate here because it depends on the desired result. A rate of 0.15 XP per turn gave closer turns for the lower lvls, but a much lower time for higher, while 0.1 stayed kind of high for the lower lvls and lower for the higher lvls. So this depends on desired balance and how fast you want troops in towns to lvl up. And also, ditto for the apprenticeship thing from the arcane explanation.
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There are a lot of little tweaks that I could have done, but this simple per turn XP rate is easy to understand and easy to balance because its easy combine rates from different sources and predict the outcome. Also remember that there are limits that can be placed to XP gained, which gives another dimension to tweak.