New cables arrived from Digi-Key. I put the T4 on stacking headers to avoid the kink.

Tried Paul's SD.h on SDIO and it worked.
Code:
Initializing SD card...Wiring is correct and a card is present.
Card type: SDHC
Volume type is FAT32
Volume size (Kbytes): 31248384
Volume size (Mbytes): 30516
Files found on the card (name, date and size in bytes):
SYSTEM~1/ 2019-09-08 11:09:22
WPSETT~1.DAT 2019-09-08 11:09:22 12
INDEXE~1 2019-09-08 11:09:22 76
BENCH.DAT 1980-00-00 00:00:00 5000000
Tried SdFat bench example on Audio Card with SPI.
Code:
Type is FAT32
Card size: 32.01 GB (GB = 1E9 bytes)
Manufacturer ID: 0X1B
OEM ID: SM
Product: 00000
Version: 1.0
Serial number: 0X1550FE3
Manufacturing date: 10/2015
FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.
write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
3731.34,2083,136,137
3734.13,152,136,137
Starting read test, please wait.
read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
3756.57,138,135,136
3767.90,139,135,135
3,767 KB/sec SPI with 512 byte buffer is not bad but not what I expected, I ask for 50 MHz clock. SCK must be much less than 50 MHz.
Ordered two more T4, FFC connectors for Teensy and these breakouts so I can make quick test setups on a perf board.

https://www.amazon.com/gp/product/B07T7FCBVS
While I am solder challenged, can't drag solder a fine pitch SMD, I can do 1 mm pitch with my 0.015 solder, fine tip iron and surgical telescope or magnifier.
Happiness!