I was convinced to wait for the Tech/Ultimate modpack... /:
Which sucks because Millenaire just came out with a new culture and I can't upgrade... the Byzantines look fun too...
Well, I upgraded to 1.4.6, downloaded the Mindcrack pack, and added Mystcraft (gotta have Mystcraft). I saved my world from Beta and copied it into a single player game with Mindcrack+Mystcraft. No bugs, no issues. My base and inventories and machines all intact and working. Visited a couple friend's bases - all good. Traveled to unknown parts and found some marble (RP2, I think) and Xycoridite. So, that is working well. Looks good to me.
Next step...I'll just do the same for the server.