Currently each of your major statistics (STR, CON, DEX, QUI, PIE, EMP, CHA, INT) can be enhanced by up to 1.5x your level from items.

Level 50 characters, therefore, can receive up to +75 in each stat from items.

Bonuses that you receive from buffs are capped separately from those that you receive from items and stack with item-based bonuses.

Spec line buffs (namely the STR/CON combination buff and the DEX/QUI combination buff) are capped at 1.5x your level. Base line buffs (such as CON) are capped at 1x your level.

Therefore if you level 50 you can received up to +75 +75 +50 = +200 increases in a given stat.

Hitpoints cap

You can received 4x your level. so a maximum of +200 HP from items.

Power cap

You can received a maximum of 0.5x your level + 1, so just as with resists, the maximum +power is limited to +26 power.