[{HVY-E}Jinxx]

Well, I'm not sure what all has been added to HSFX 4.1 since UP 1.8 came out before it, but the next UP will contain HSFX4.1 and a little bit extra.Through the mod enabler you will actually be able to enable pure HSFX 4.1 in the new UP, or add the extra stuff, so the new UP is going to basically be HSFX 4.1+.

You're partially right. UP1.2.5 was rolled up into HSFX 4.1.

So the correct series of events was:
UP 1.0
UP 1.2
UP 1.2.5 (never release to the public)
HSFX 4.1

To my understanding, all further releases will be HSFX 4.xx or 5.xx (Can't wait for the new stuff!)

S!