True actinics are roughly 420nm, while the Blue Plus are 450-460nm. The actinics will be more of a purple / blue while the blue plus are more of a solid blue. Because of this the true actinics are going to have even less punch, and be even less noticeable while the halides are on. While the actinics are my personal favorite color of blue supplementation, they're just really hard to run when you only have two of them in T5 trying to supplement your 2 x 250's. I'd still stick with the Blue Plus.
For acclimation over that tank I'd start the fixture around 15" - 16", and run the halides for 4-5hrs per day, maybe running the T5's an hour in front of that and an hour in back of that. I'd try to work the halides up to 6-7hrs per day at around 12" - 14" height, again with the T5's being an hour in front and an hour in back.
Keep in mind that every 3" you raise the light will have approximately a 90% decrease in light reaching the corals.