Nice one! Great contribution!
Looking at the sources, I can say they're the latest CPU filter editions I used in Kega Fusion plugins.
There are three xBR flavors: squared, semi-rounded and rounded. In Kega plugins I named them as "a", "b" and "c", respectively. These flavors differ mainly in how fonts and huds are treated.
In your sources, you've used "b" flavor for 2xBR and 4xBR, and "a" flavor for 3xBR. They differ only by these lines (look at the lines 127, 342 and 544 in your sources to see the flavors you're using):
"a" flavor:
if ((e<i) && ( !eq(PF,PB) && !eq(PF,PC) || !eq(PH,PD) && !eq(PH,PG) || eq(PE,PI) && (!eq(PF,F4) && !eq(PF,I4) || !eq(PH,H5) && !eq(PH,I5)) || eq(PE,PG) || eq(PE,PC)) )\
"b" flavor:
if ((e<i) && ( !eq(PF,PB) && !eq(PH,PD) || eq(PE,PI) && (!eq(PF,I4) && !eq(PH,I5)) || eq(PE,PG) || eq(PE,PC)) )\
"c" flavor:
if (e<i)\
I can't say which of them is the best. It depends on taste. You probably like more the "a" version. You could try adding all flavors to each, making a total of 9 xBR filter options.