Looks like 4MB erase block, maybe a 128kB block and 32kb page. 7au, several runs done as there was some variation in numbers, these are typical runs. 

CompactFlash ATA device
Model Number: SanDisk SDCFH-004G
Serial Number: AAZ091113183311
Firmware Revision: HDX 7.07

pictsidhe@Miner-D:~/flashbench$ sudo ./flashbench -a /dev/sdb --blocksize=1024
align 1073741824 pre 763µs on 980µs post 766µs diff 215µs
align 536870912 pre 884µs on 1.18ms post 888µs diff 290µs
align 268435456 pre 843µs on 1.09ms post 840µs diff 248µs
align 134217728 pre 837µs on 1.03ms post 782µs diff 223µs
align 67108864 pre 870µs on 1.12ms post 835µs diff 269µs
align 33554432 pre 810µs on 1ms post 752µs diff 222µs
align 16777216 pre 864µs on 1.15ms post 862µs diff 287µs
align 8388608 pre 802µs on 1.05ms post 807µs diff 247µs
align 4194304 pre 773µs on 1.03ms post 808µs diff 240µs
align 2097152 pre 786µs on 886µs post 785µs diff 100µs
align 1048576 pre 782µs on 909µs post 778µs diff 129µs
align 524288 pre 781µs on 885µs post 771µs diff 109µs
align 262144 pre 779µs on 886µs post 778µs diff 107µs
align 131072 pre 775µs on 882µs post 749µs diff 121µs
align 65536 pre 779µs on 882µs post 779µs diff 103µs
align 32768 pre 773µs on 895µs post 777µs diff 120µs
align 16384 pre 779µs on 848µs post 778µs diff 69.5µs
align 8192 pre 779µs on 843µs post 779µs diff 63.5µs
align 4096 pre 775µs on 859µs post 780µs diff 81µs
align 2048 pre 774µs on 843µs post 776µs diff 68.1µs

pictsidhe@Miner-D:~/flashbench$ sudo ./flashbench -O --erasesize=$[4 * 1024 * 1024] --blocksize=$[256 * 1024] /dev/sdb --open-au-nr=7

dd tests, 256MB file size:

Block: 2K 4K 8K 16K 32K 64K 128K 256K 512K 1M
Write: 1.5 MB/s 2.7 MB/s 4.9 MB/s 12.2 MB/s 18.0 MB/s 22.4 MB/s 26.0 MB/s 26.3 MB/s 27.5 MB/s 26.5 MB/s
Read: 3.7 MB/s 6.7 MB/s 11.0 MB/s 16.3 MB/s 21.5 MB/s 25.3 MB/s 27.8 MB/s 28.1 MB/s 28.2
MB/s 28.3 MB/s