The difference between 288 RPM and 300 RPM is only 4%. This is well within the range of frequency error that a floppy disk decoder should, or rather, needs to be able to tolerate. a8rawconv doesn't have a problem decoding 300 RPM disks at 288 RPM timings, as you can actually give it a 360K DOS disk and it will decode 9 MFM 512 byte sectors per track even despite the difference in timing. The other way works as well: I just wrote out a physical disk using 4us @ 300 RPM cell timings instead of 4us @ 288 RPM timings and my 1050 drive happily booted DOS 2.0S. And, as I noted, I and many other people successfully read Atari disks on PC controllers that did not have clock settings for 4us @ 288 RPM equivalent cell timings.
Keep in mind, FM only has at most one 0 bit between pairs of 1 bits, so the decoder has a lot of chances to adjust its tracking. If your decoding algorithm is unable to accommodate a 4% difference in cell timing, then something is fundamentally wrong. I can detune a8rawconv's decoder as far as 10% off of ideal and still pull clean sectors off a real disk image, and I'm pretty sure it can still be improved.