With an SSD the only thing it affects is high threaded 4K random reads in benchmark results due to lack of NCQ. I’ve been running and SSD in IDE-mode for 3 years and I’ve not noticed any real-world performance problems. As Albert alluded to, on older BIOS’s (pre-UEFI) the IDE boot process can become a little slower, with newer BIOS/UEFI I haven’t found this to be noticeable.
AHCI has always given me nothing but headaches so for me having a small drop in SSD performance in very specific use scenarios vs. having one less buggy controller interface with bad compatibility causing annoyance is a clear choice of the former.
So does it detect the drives in IDE mode, and maybe fix the issue with the jitter scans?