You can cascade two PLLs. Probably even more if necessary, but your clock jitter might become too much.
Yes, it's possible to get exact 800/858 ratio by cascading 2 PLLs (e.g. (40/78)*(20/11)) but it's not a generic solution which works for every ratio.
I don't know if this has been reported, but with FW 0.71 there is a bug on using odd horizontal scanlines with lineX3 mode.
Scanline will be set on the 2nd line instead of the 3rd line as expected.
Good note - I'll add that to bug list.
Also, while I tested some arcade PCBs (M92, System 18, Toaplan V2, SPI) I had only 1 issue : the SPI gave me a black screen (on a BenQ G2400W) without any red led, either through AV1 RGBS or AV3 RGBHV (through Sync Strike), the only way to make it work was to upscale it first to 31khz (Micomsoft DISPL to AV3 RGBHV).
SPI (Viper Phase 1) worked on an old fw so I'll need to check that again when I have a chance.
I got my OSSC today and I have been having an issue that I haven't read here yet.
When I use the SNES (while playing MegaMan X3) I get an issue that when I shoot a charged up shot the screen desyncs and goes back for a second. I tried on 3 tvs and all did this. I then hooked it up with my DVDO Edge and it does the same thing...
So then I hooked it up with my sync strike and it works fine even in line trippler mode...
The genesis works perfectly.
The PSX however is having the same issue on SCART as the SNES on Symphony of the night.
Is this normal?
Those are usually signs of a low quality cable which has insufficient shielding, but you can try setting sync LPF to max and possibly reduce sync vth to see if it helps.