Could I get some help determining an EL?

[whatisitgoodfor]

I've been wanting to toss this encounter at my PC's, but I'm having a bit of trouble deciding how hard its going to be for them.

Tunnel of Doom: A tunnel about 200' long, fully submerged. The tunnel is fairly large, about 25' to a side. When the PC's meet the 1/2 way point, I'm going to have an advanced Saughin hunting party come out of some hidden side tunnels.

I was planning to make the hunting party be a cleric, a rogue, two rangers, and a Fighter.

The party is made up of a Mnk12, Ftr5/Wiz1/Blade6, Brb7/Bear5, Clr12, Rog10/Shadow2, and a Drd6/Rog6. All of the characters are a little bit maxxed, but nothing outrageous, and the character wealth is close a little low.

So, the question is what levels should the Saughin NPC's be, and how can you determine what putting the encounter in this kind of area does to the EL?

Oh, BTW, I'm planning to spring the whole partially submerged temple on them with little to no warning.

Thanks in advance people.

 

[GuardianLurker]

It sounds like this isn't the climatic battle (or even a major turning point/mini-boss), so I wouldn't go any higher than EL +0 (that's EL 13 = 12 + 1 [for the large party]). Considering the characters are going to be underwater at that point, which I assume is an alien environment for them, I'd even knock it down an EL or two, and give the PCs an Ad Hoc XP adjustment upwards.

In general, I try to have the "big boss" be EL+4, the "small boss" be EL+3, one or two "critical points" be EL+1 or EL+2, and the remaining encounters be EL+0 or less.

Here a chart I use for planning :
14 "points" per level
EL/Points/% Resources/Notes
+6/8/160/Most likely dead
+5/6/120
+4/4/80/"50/50" point
+3/3/60
+2/2/40
+1/1.5/30
+0/1/20/Normal
-1/0.6666666/15/Tough random
-2/0.5/10
-3/0.3333333/7/Easy random
-4/0.25/5/Why bother?
-5/0.1666666/4
-6/0.125/2

[edit :fixed table]

 

[whatisitgoodfor]

Sorry, I guess I should have explained this earlier. I am familiar with that EL chart, I use a modified version of it myself (I treat an EL +2 encounter as a "good" encounter. +1 for a large party, and +1 for those darn tacticians in the party.).

What I'm not certain about is how much an alien environment like this one will add to the EL.

Does anyone have a good way of determining that?