I do not have that much stage knowledge, but "a little" is how much? 1.4 GHz is 3b+, which already OC (like Athenon Black Edition, am i right?), so 1.5 GHz? 1.6 GHz?
As much as it will handle. Also, gpu_freq and sdram_freq are just as important as arm_freq.
10-bit 1080p HEVC works on Raspberry Pi 3 with LE 9.
Get a Raspberry Pi 3 B+.
but, in my country people are selling those for such an unreasonable price
Why not import it from China for a reasonable price? Way better option than buying a crappy videocard for a crappy PC 
Raspberry Pi 3B+ is a great choice if you don't need 4K.
Use beta 8.95.1 or current Milhouse build.
Do you know what is actually the reason why some hardware supports it or not?
I believe this has something to do with the clock generator logic.
Wasn't that general issue with Kodi?
Some hardware is not capable of smooth playback of video with fractional frame rate like 23.976Hz. For example, all pre-Haswell Intel GPUs play 23.976Hz video at 24.000Hz and you get a repeated frame every 40 seconds. AMLogic also had this issue (but AFAIK it was fixed with some kernel patches).
I was wondering if Allwinner hardware is capable of properly displaying 23.976 fps video. I can't test this myself because I don't have the hardware (yet).
How well do those Allwinner devices handle fractional frame rates? Are there any issues?
jernej Do you have any ETA when deinterlacing will be implemented?
Save EDID to a file (tvservice -d edid.dat), copy it to /flash, and put hdmi_edid_file=1 in config.txt.
What UPnP bug?
That image will not work. Old kernel and old firmware.
It should be tested on a current build of Kodi 18. I can check if it works on a current Milhouse LibreELEC 9 build if you upload a sample to Google Drive, Dropbox or something like that. Or you can install the latest Milhouse build (or v8.90.009 ALPHA build) and test yourself.
Can you upload a small sample?
Use DVI to HDMI. But how do I get audio?
Did you try it? Not sure about your Foxconn NT3700 but modern videocards can output audio over DVI as long as you use DVI to HDMI cable.
I'm currently using kernel 4.19.7 with the "MUTEX_FLAG_HANDOFF 0x00" hack on a Raspberry Pi3 and it works well. Kernels 4.8 and 4.9 also work fine.
Well, it didn't pass the antenna cable "hot unplug" test that I do to accelerate the tuner failure.
@jahutchi I get this build error
CC [M] drivers/media/usb/dvb-usb-v2/dvbsky.o
drivers/media/usb/dvb-usb-v2/dvbsky.c: In function 'dvbsky_i2c_xfer':
drivers/media/usb/dvb-usb-v2/dvbsky.c:117:27: error: expected ';' before 'if'
mutex_lock(&d->i2c_mutex)
^
;
drivers/media/usb/dvb-usb-v2/dvbsky.c:119:2:
if (num > 2) {
~~
drivers/media/usb/dvb-usb-v2/dvbsky.c:115:15: warning: unused variable 'obuf' [-Wunused-variable]
u8 ibuf[64], obuf[64];
^~~~
drivers/media/usb/dvb-usb-v2/dvbsky.c:115:5: warning: unused variable 'ibuf' [-Wunused-variable]
u8 ibuf[64], obuf[64];
^~~~
make[5]: *** [scripts/Makefile.build:304: drivers/media/usb/dvb-usb-v2/dvbsky.o] Error 1
make[4]: *** [scripts/Makefile.build:544: drivers/media/usb/dvb-usb-v2] Error 2
make[3]: *** [scripts/Makefile.build:544: drivers/media/usb] Error 2
make[2]: *** [scripts/Makefile.build:544: drivers/media] Error 2
make[2]: *** Waiting for unfinished jobs....