I've been having a look at stats by doing some item juggling whilst I wait for the new day. The game system seems fairly transparent:
Encumbrance = (STR+CON) X 10
Attack factor (melee) = STR + weapon attack factor - back rank penalty (if applicable)
Attack factor (ranged) = AGI + weapon attack factor - back rank penalty (if applicable)
Note: slings appear to have an undocumented back rank penalty of 4!
Defence factor = AGI + armour factor
Damage = weapon damage
Hit points and magic points seem to rise randomly on levelling, with a bonus based on the relevant stat (CON, INT or DIV). INT and DIV may or may not affect other less visible aspects of the game system, like luck - perhaps a test would be to record critical hit rates, and see if the priests do any better..
Movement factor affects the cost of entering wilderness squares. The party movement factor is, like party level, the average of individual members. Potential movement factor (the value in brackets) is CON/5 rounded up. I think actual movement factor is derived by taking your unused encumbrance as a fraction of the total encumbrance, multiplying it by your potential movement factor, and rounding to the nearest whole number but it could be something a little more complicated.
One odd result from this choice of mechanic, is that the STR/CON pumping dwarf fighter is much, much speedier than the stereotypical elven archer agility fiend.
With regard to the effect on speed in the wilderness, I've had a look at parties of movement factor 2 and 3 so far:
Terrain Movement cost @Factor 2 @Factor 3
Fields One turn One turn
Marsh Two turns One turn
Medium forest Three turns Two turns
Dense forest Four turns Three turns
Hill Five turns Four turns
Lake Six turns Five turns
Mountain Seven turns Six turns
So your movement cost over mountain is nine minus your party movement factor (with a minimum cost of one), assuming things are as simple as they look.