I did modify my U-boot slightly (see here Fixing U-boot to support boot from NVMEs) to support some of the SSDs that I have. With this change the boot is pretty fast. Under 30 seconds to see the login prompt.
As for the speed… here is one run that seems to be typical using the following command
fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=test --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75
DataRam
-----------
test: (g=0): rw=randrw, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=64
fio-3.1
Starting 1 process
test: Laying out IO file (1 file / 4096MiB)
Jobs: 1 (f=1): [m(1)][100.0%][r=178MiB/s,w=58.8MiB/s][r=45.6k,w=15.1k IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=3478: Sat Nov 16 07:05:02 2019
read: IOPS=45.2k, BW=176MiB/s (185MB/s)(3070MiB/17403msec)
bw ( KiB/s): min=165576, max=184704, per=100.00%, avg=180934.65, stdev=3336.51, samples=34
iops : min=41396, max=46176, avg=45233.62, stdev=833.94, samples=34
write: IOPS=15.1k, BW=58.0MiB/s (61.8MB/s)(1026MiB/17403msec)
bw ( KiB/s): min=55032, max=62108, per=100.00%, avg=60473.24, stdev=1275.30, samples=34
iops : min=13758, max=15527, avg=15118.35, stdev=318.85, samples=34
cpu : usr=24.37%, sys=69.26%, ctx=16876, majf=0, minf=8
IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=100.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, >=64=0.0%
issued rwt: total=785920,262656,0, short=0,0,0, dropped=0,0,0
latency : target=0, window=0, percentile=100.00%, depth=64
Run status group 0 (all jobs):
READ: bw=176MiB/s (185MB/s), 176MiB/s-176MiB/s (185MB/s-185MB/s), io=3070MiB (3219MB), run=17403-17403msec
WRITE: bw=58.0MiB/s (61.8MB/s), 58.0MiB/s-58.0MiB/s (61.8MB/s-61.8MB/s), io=1026MiB (1076MB), run=17403-17403msec
Disk stats (read/write):
nvme0n1: ios=778690/260197, merge=0/0, ticks=565565/252813, in_queue=12484, util=99.35%