Cap of 25% critical chance refers to the maximum percentage you gain from crit rating. So...
- passives/buffs that add to crit rating will bring you closer to the 25% mark, but not over it.
- passives/buffs that add to crit percentage are added to the percentage you get from crit rating. This can (and will) exceed the 25% mark.

So, you'll want to bring your crit rating close to 630k, to get as many of these tasty critical hits as possible. Certain other classes like cappy may give you a crit rating buff, so it is usually fine to be a bit below 630k.