They give the same lift but they each do it differently. The way the out of the pack spacer works is it lengthens the whole coilover assembly the thickness of the spacer. When you try to stuff a complete assembly that is rougly ~2inches longer into a space that wasn't designed around that extra 2 inches, something has got to give.
Now, the limiting factor of the front droop is not the coilover itself anymore, it is now your balljoints. They are going to be under a lot of stress because the "extended" coilover pack is trying to push the front suspension farther down then it will allow. They have a little extra travel built in, but not enough to support the way those spacers work. The only way you will get that assembly back in the truck is to unbolt the lower balljoint and drop the lower arm down. That alone should show you that the lower and upper balljoints won't travel far enough to support this "longer" coilover asy.

The in the pack spacers are harder to install because it requires you to disassemble the coilover asy and install the spacer between the top-plate and the coil spring. The way these spacers work is that they basically preload the coil making it harder to compress it and therefore giving you lift. The cool thing about it, the complete coilover pack is still the same length and it will bolt in like the stock coilover will. It will not over-extend the balljoints and cv's because you are not going out of the factory travel range.

Here is some extra reading for you Link .
Go to the articles section and read the 2 articles there. They have some good information about lifting our trucks.

Hope this helps you understand the differences between the 2 types of spacers, how they work and how they can affect your truck's suspension.

PS - You can still sell those spacers....... <img src="/forums/images/graemlins/wink.gif" alt="" />

The in coil spacers are better. They are some work to install because you have to compress the coils a lot to get the shocks on. But after you do they are easy to put on. Donahoe racing has some spacers that replace the top plate and work like in the coil spacers. You can get them there or at URD racing. You can find some like them on ebay for $59. Do not use the other spacers. Get the ebay Doetch or the Donahoe spacers and they replace the top plates.

To get a new top plate on you are going to need a spring compressor anyway. So sell your other spacers and rent a spring compressor and get some in the coil spacers. Like I said the ebay Dotesch or the Donahoe replace the top plate. The lift is 2.5 inches.