Can you win at level 8 in Munchkin?
From the Munchkin Rules:


  The first player to reach Level 10 wins . . . but you must reach Level 10 by
  killing a monster, unless a card specifically allows you to win another way.


The only requirement it gives is that you kill a monster to reach Level 10, it doesn't say you have to be Level 9 when you kill it. The only other rules about winning say you can't reach Level 10 by selling loot or playing a Level Up card.

From the Munchkin FAQ:


  Note also that ANY level gained as a result of killing a monster counts as the winning level. If you have a Race or Class ability that lets you get an extra level after winning certain combats, that level can be the winning level.


This supports the idea that you don't have to be Level 9 when you kill a monster, you just have to get to Level 10 as a result of killing a monster.