does it apply to both divine and arcane or only arcane?

<font color = shadowed cyan> Im pretty sure its both of them but ill need some one to clarify. im like 95% sure it is both though. test it and find out.</font>

it applies to both unless you have the IIRC lvl 40 spell mod which allows them to go up to 40 and IIRC uncaps capped spells (like fireball will do 1d6 per caster level instead of 1d6 per lvl MAX 10d6)

Yep. Spell 50 mod. Very fun. Having a Lightning bolt do over 100 damage is quite satisfying.

Little understood fact: probably makes blades better than fighter/mages. Since blades can shoot up in levels, and mages only get 1/2 XP, blades' spells are far more powerful sooner. Would apply to any bard, come to think of it.

are you sure?

i had a level 16 haerdalis, and he was utter -crap-

so i just let him die in the twisted rune area (died from wail of the banshee, how WEAK)

With the Spell-50 mod, yes. The game calculates your highest spellcasting level when it calculates those effects. Bards fly up there in levels, based off the rogue XP totals. As such, their spells become far superior to a multiclass mage's. Combine that with their above-average combat skills, and with the Spell-50 mod you have a winner. I would read up on Scythesong's Guide to Blades, on Sorcerers.net, if you want to use a blade well.