The 750Hz peak is tamed down quite a fair bit. Using another sized back chamber, size of a bucket or so, this happened:

That dip around 1KHz is filled in a little bit. The compartment which the horn will be installed in within my tower, I have a feeling that size is going to tame the peak a little bit further still.

Overall I am very happy with the outcome now. Looks like I'll have to cross around ~600Hz, possibly a little bit higher. It will be actively crossed using Behringer CX-2300/4th order LR filter, its got adjustable xover freq in case I fiddle more and get more low end out of it.

Since I used compression ring to get it down to 80mm diameter throat from 110mm, and I am gonna keep using 80mm as thats what I want; When I build a pair for it, do you think I should just make one more horn like this one with 110mm and use the comp ring to get it to 80mm. Or should I make two new horns with a real 80mm throat from the beginning? The dispersion could be a little wider using proper 80mm diameter throat (because I can get a little bigger wall angle), but I dont want to risk it not working right. Which should I build?