Sanguinary Priests - Are they worth the points?

Just some math-hammer on Sanguinary Priest, to decide if I want to put them in my army.  First, since they are only range 6", I probably want to have one per unit, as I am probably not marching down the middle of the field (we are not orks after-all).

First, I am going to calculate them with jump packs.  A priest with JP cost 75 points, about 4 ASM.  Assume that 1 in 3 in going to make the save.  This means that my unit can basically take 2 extra wounds. (I take 3 wounds, save 1, which leaves me with 3 marines, take 3 more wounds, save 1 again).  Add in the Sanguinary Priest himself, and I am basically getting 3 marines for the price of 4. 

So let's looks at 10 marines.  10 marines take 3 wounds, save 1 to FNP, leaving 8.  3 more wounds, 1 more save leaves 6.  3 more wounds, 1 more save leaves 4, 3 more wounds leaves 1. So it takes about 13 wounds to kill them all, instead of 10.  Add in the Priest himself, and I am getting 14 wounds for the price of 14 marines.  So it's a wash (except for the slightly improved stats in had to hand).

All of this is assuming again that the Priest is the last one killed, and that the enemy is not using Instant Death weapons.  If the enemy is using a lot of plasma, it will take less hits to inflict this number of wounds, but the number of wounds in the unit doesn't actually change.

Edit: While trying to calculate the most efficient scoring choice, I thought of another metric to measure this by.  A tactical squad costs 170 points, and it takes, on average, 90 bolter shots to kill all 10 of them.  This comes out to about 1.89 points per shot the unit can soak.  Adding a priest bumps the unit up to 220 points, but the unit can take 140 shots before being destroyed.  This comes out to about 1.57 points per hitpoint.  So it is slightly more efficient to take a priest in a tactical squad.  I don't think this invalidates my previous, empirically based deductions, since we cannot spend fractions of points, but it does show that a priest could be work it (these wounds do not the count the priest itself, who would still be alive at the end of these 140 shots).