There are many posts on "what size QCTP?" Check your elevation off the compound. I put an "E" on my 11" - mainly because I wanted to use 3/4" tools. I knew it was going to be close, but I assumed I'd be able to sort it out. It was too high, so I skimmed the bottom surface of the holders (~0.075"). I worked out the amount to skim so that the holders for the main tools would sit right down touching the compound - that way no height adjustment device would be needed (perhaps it also has a bit more support?). After all, for the main tools - they will reside in that holder for as long as I own the lathe.
I'm sure the "E" would work great. Perhaps you could make the "B" fit, but since it is a bigger lump of iron, it would be tougher to get in close on certain set ups. Regardless, you can still do the trick of sitting the holder right down on the compound by gluing a shim to the bottom of the holder.
I did not buy the Multifix, the imports are comparable in price to other style of import holders (no complaints - sample size of one, it works great).
I suggest you drive it the way it comes, make chips for a couple years, upgrade as needed. A down side of the multifix style is that it would be tough to make your own holders (copying that spline) - the dovetail is much easier to make. I made some CXA holders for the 15" lathe - sort of to prove I could (however the holders are pretty cheap, so now I buy them as needed).