OP,
Yes there is a difference when you use the 3M Blue pad with the Ultrafina. It has special oils in it that work inconjunction with the Ultrafina, hence that is why they tell you not to wash the pad, only clean on the fly with a towel or with a brush.
I know 3M lost their patient on the "waffle" style, which is why we are seeing a bunch of companies releasing their own version.
Now I primarily use 3M pads soley. I use the white for compound, black for polish/swirl removale, and blue for jeweling. Granted the pads seem to cost more but if you shop around, you can actually find 3M pads for cheaper/same prices as the LC Waffle pads. That is why I haven't bought any of the LC pads. I use both the 4 in and 8 in 3M with my Flex PE-14.
I have rarely come across a situation where the 3 colors offered by 3M didn't work. If that happens, its usually when it comes to polishing super soft paints. For that I'll use Buff and Shine in the colors of Green, Black, or White. AG doesn't carry these yet but I wish they would. They last longer, finish better and feel better than any of the LC pads I've used in the past. Another pad by B&S I use all the time for 1step/cleaner wax is the Yellow with D151. Works wonders.
3M pads seem to cost more, but there is a difference. They work a lot better. I have used/tried a LOT (maybe over 30) different pads over the years and just tried the 3M about 5 months ago after I was doing custom detailing for a body and that's all they were using. I was simply blown away by how well they worked.
The LC waffle pads look identical to the 3M one with the addition of the orange pad. I'm guessing that this is the "3M Black" and that the LC Black is like the B&S Green/Black. (Hope that made sense).
As far as 5.5 pads, I haven't seen or heard of any being out. I'm assuming that you would want them for DA application, and I know for body shops, no one uses a DA. They all finish (or try to finish) down with rotary so there is no real need for the smaller pad.
I would rec you try the 3M and just get a feel for it. Its worth at least trying especially if your using the UltraFina finishing Polish. Its a great polish and does wonders to black paint. The only downside is I was told by my 3M rep, that it does contain fillers and was designed specficily for black paint. I've been able to chemically strip the paint and still haven't found that it covered anything/no swirls were there. I don't know how this would effect LSP coverage. I feel its kinda redundant to jewel with UF then strip it off and then apply LSP. I haven't had any problems with going straight from UF to LSP.