250 Six banger exhaust question

[Hair]

I'm running a stock 250 except for a set of headers and an HEI that I added.

I finally got it out the other day for the first test drive (open headers).

It ran fine, but felt like it had lost a lot of low end power compared to what it had in stock fashion.

I figured that it was due to the open headers. Am I correct in thinking this?

If so, here's my delima, I was planning on running dual exhaust from the headers out the back using 2.25" pipe and two turbo mufflers. Would that be too big? Originally I think it only had like a 1.75" single pipe. Should I maybe go with 2" pipes or maybe 1.75" or will the 2.25" work fine?

I was going to use 2.25" because the headers came with a 2.25" adapters.

I've heard both, some say that there's no such thing as not enough back pressure, but I've noticed from personal experience that on smaller engines especially (like motorcyle engines) no back pressure DOES cost power. I've never messed with a straight six before, until now, so I just don't know.

What about it, will dual 2.25" be okay?