The only problem is SP19 is the cutoff for future upgrades... correct?
RANT: Why retire OVSD? I'm getting a very sour taste in my mouth with HP. As for the next 'wave' of Peri-HP-Desk the pricing structure is so far off the scale from reasonable, not to mention admin intensive... anyway, that's another discussion.
Actually the point of no return is SP18. If you are on SP19 you have crossed it (since only SP17 can be upgraded to 5.1).
I don't see any reason for going to 5.1. OK, the SLM module is presumably better but otherwise 4.5 SP20 beats hands down v5.x. Dynamic forms, unlimited custom fields, the e-mail service call entity... and it's lighter and it's faster.
In any case the bug you 've described earlier is ITSM008529 and it is indeed fixed on SP20.