How much power do engine mods yield?

Oh-Oh

I heard it. 50% hi-way at 55mph.
Ima thinkin 3.55s might be too much. That'd be about 2750rpm. I know the slanty is pretty smooth(by design), but 2750 is still up there. 3.23s will pull it down to around 2500@55. If you are concerned about fuel economy, then that 250 rpm is valuable. If you are spending a lot of time on the hi-way then even the 3.23s might be too much.
In that case if it were mine, I would bump the Scr up.With no other mods, yet. I would bump the Dcr up to 8.5 or so. Then a sharp tune.
That is what I did to the 225 in my 80 Volare. This gave me a lot more punch off the line, and I was able to keep the 2.76 gears.Then later,I swapped in a wide-ratio tranny with a loc-up. This gave me even more snap;and hi-way cruising with 2.76s, a loc-up and taller tires gave me 2270@65.
In this case the new low gear in the tranny gave me 12% more take-off torque, the loc-up T/C was about 300 rpm more stall with the higher c/r, so thats more snap. And the additional engine c/r brought yet more torque to the table.
With just these changes, The take-off was snappy,and the hi-way economy was much improved. The wider tranny ratios, were hardly noticed.
I spent a lot of time on the tune, but it was well worth it. I still have this car, but the body is gone, so I didnt register it this year, for the first time since 1995.
So in this case, Torque was increased with compression. Take-off was improved with; engine torque, TC stall,and tranny gearzzzz . Rpm on high-way was decreased with the loc-up. Fuel economy was improved with the increased compression, the lower running rpm and the tune.
Notice, no where is there a cam or a carb or an exhaust change.
The engine will have the same personality as before, just bigger. I venture to say that 80% or more of the time, your engine will be spinning at less that 3500rpm.If thats true,IMHO, it doesnt need a cam or a carb and perhaps not even a bigger exhaust.
Eventually, I installed a bigger, solid-lifter cam. With it went the Super-six stuff. Well, that was a bit of a step backwards, in terms of take-off. Yeah, it was better able to pass at higher speeds, but it was definitely softer on the take-off. It really wanted gears. But it wasnt soft enough to warrant changing. I left it that way for many years.
This was my experience.
Again, all the best to you,whatsoever you choose.