So, the dungeon level/depth is 4. What do I roll for the difficulty on a D10? 3!
It kind of feels a bit like a non choice - would you like to go to the marginally less dangerous dungeon?
Also since their are some party member objectives in there, I I realise I kind of have to hurumph that the objectives are in either dungeon. Also, what if they want to go to the other one? I guess I have to say it's a meta game choice - harder or easier is a player choice, not a character choice.
I guess one level of difference can make a difference. In rolling the level three stuff, if it was more powerful than the level four creature already there, I switched the two around. Also I only made the first leg of the dungeon have a different set of monsters for each.
On a side note, I have a series of treasure rooms in this one which are time sensitive (so is the end objective, but in more of a made up as I go way, not a written down time). Each has a marking near them that the players are told at the start of the dungeon. To see if they can remember when they come across the marking (not as easy as you might think). There are also four rooms where there is a way of getting the treasure without fighting. It's also possible to get to them without fighting.
Also have a bunch of other ideas I'm trying out in the dungeon, as I tend to do - looking to work out some special combination of effects!