...and to further muddy the waters - based upon my recent testing (rebuilding some old S&T's that were stripped for parts), it appears there can be significant variations in speaking speed between TMS5200's as well.
I have a CD2501E (TMS5200 equivalent - just the internal TI part number) that speaks more quickly than normal - coherent, just faster.
I also have two TMS5200's I just recently received from ArcadeShop. One of these has what I'd consider the typical/normal speed (it matches up speed-wise with the original TMS5200 for this board), but the other feels significantly slower.
As it happens, my test S&T board is configured for Flash Gordon as well, so I figured I'd make a few videos for comparison.
Note that the speed follows the chip - no matter how many times I tested it, the speaking speed was consistent.
This might explain why I've played some pins with a S&T and thought the speech didn't sound quite right - curious if others have noticed this as well?
YouTube playlist with all three videos: https://www.youtube.com/playlist?list=PLdnHnpSIQSFjmsPGYCkOR7PlOvAy6udpy
If you simply can't find a TMS5200, the 5220 would be better than nothing, even with the distorted bits I suppose.