Johnny,
You will want the full merge.
I had put together a list of the power outputs from the two dynos comparing merge with non-merge.
The top two is the non-merge run with percent gain and total hp gain under that.
The last two are the same table with the full-merge header.
For this chart, you can pretty much ignore the raw data (top two rows on each data sample) what we are looking at here is %increase, and actual increase because that data makes the dyno or correction factor much less relevant and allows you to truly compare the two styles of header. Also, check out on the far right the total "HP/TQ Gained" for the two different runs. Look at the increase for the full merge. It's undeniable buddy.
Disclaimer: I put these numbers together using my eyes. The chart below is far from perfect, many of the points might appear off or incorrect, I had to make do with what I had. For the purposes of this chart it would have been nice to have a bit more smoothing on the graph, but no big deal just keep it in mind when you are looking things over. I used a ruler and fine graphing lines to plot this table so it is really the best possible without real numbers.
Dudeman