how stable depends on your line
depends on your SNR and line attenuation

I don't think many condo got 8Mbit unless you are really lucky.

No problem for non-P2P download, it will reach 8Mbps.
Obviously it's not supported

Used to be 20+dB for SNR.

is that before upgrade to 8Mbps? or already on 8Mbps?

if before upgrade, then what speed you were upgrading from? 1Mbps? 4Mbps?
cos raising hardcap speed always reduce snr rates
if already 8Mbps, was fine but now getting low snr, then it could be wiring issue or problem at TM's side

yeah

normally snr is more than 15 for stability
best if you have 20+,  but too high also not good?
but attenuation lower is better

if snr high but attenuation also very high like 50 above, also not good
higher they set the speed rate, snr goes lower, attenuation may go higher or on line quality or interruptions or the copper line length

as long as you have the right speed and stable

then it's fine, doesn't really matter if rates are not so good

if you have problems then should call them see what they can do for you,

if they couldn't fix it due to too far or technical issue, mostly ask you to downgrade for lower speed