- Whether the thread has been front paged.
- Whether you're one of the first replies.
- How deep in a thread you reply.
- The popularity of the subject of the root node.
- The actual content of your post.
If only you could see all the reputations of all the nodes in a thread, then you could compare. A reputation of 15 where all the other posts don't get above 10 is likely to be better than a reputation of 25 where all the other posts score 40 or above.