Flame Golem - Damage increased per gem level or not?

Does Flame Golem get damage increase like Zombies or like Spectre? Looking at the wiki http://pathofexile.gamepedia.com/Summon_Flame_Golem, it seems that its damage is set according to zone level, not gem level (look at the table in the bottom of the page). If this is correct, its max base damage is 1644–4110 regardless of level.

That table is the monster level of the golem, not zone level. It does increase with gem level.

Ok, thanks. Is there a way to tell what the relation is between the gem level and Golem level?

Yep, it's the column after gem level in the first table. It's basically the level requirement of the gem except that it keeps scaling.

At gem lvl 20 the golem itself is lvl 70.

Ahh, now I see. Thanks!

Great this was some of the information I was looking for too.

So a level 20/0 gem will summon with these base stats
Level 70
Life 6776
A.S. 1.00
Damage 619–1547

How do we calculate the damage from the 3 spells
- Magma Ball - Projectile AoE spell, 100% Fire
- Flame Wave - AoE spell in a ~120° cone, 100% fire
- Immolate - Spell that releases a barrage of 4 piercing projectiles, 100% Fire

For Magma Ball the projectile will have a chance to do 619-1547 fire damage
Flame Wave will have deal 619-1547 fire damage each tic
Immolate will do a barrage of 4 projectiles each doing 619-1547 fire damage

Would it be better to scale up with a 21/20 gem or a 20/23 gem?

Am I correct in assuming that a level 21/20 gem would provide
Level 72
Life 8959.2
A.S. 1.00
Damage 820.8–2052

And a level 20/23 gem would provide
Level 70
Life 8334.48
A.S. 1.00
Damage 761.37–1902.81

If these assumptions are correct then the +1 level is the gem I want to get correct?