Here's my data:

3,400 sft home, 4.5 baths
4 people (two are 13 and 9 yo)
municipal water
1.5" main copper water line

hardness 15gpg
iron none
manganese none
PH 7
TDS 550ppm
sodium 101ppm
chlorine 0.5ppm
SFR 12gpm (7 gallon container took 35 seconds to fill)

I know I want to get Fleck 7000SXT, primarily due to my 1.5" main copper water line and some of the feedback I've read.

Question: I'm debating on the size of 1.5 ft3 (48K resin) and 2.0 ft3 (64K resin) because one supplier said 1.5ft3 would be too small to use with 32mm distributor pipe as water will flow through the resin media too fast and recommend to at least go to 2.0 ft3. Another supplier said since 7000SXT comes with 32mm distributor pipe as a default so it should be ok with 1.5 ft3 (48K) system. Which is true?

The only reason I thought of 7000SXT was due to the 1.5" main copper line that I have and would like to minimize the pressure drop. So for my situation is it better to go with:

1) 7000SXT with 1.5ft3 (48K) with 32mm pipe
2) 7000SXT with 2.0ft3 (64K) with 32mm pipe
3) 7000SXT with 1.5ft3 (48K) with 1.05" pipe

???

Thanks in advance for your help.