So just as a future aid to anyone looking for the same advice...

TIA-BEG on an ATR 72...my bag was weighed at check-in, I was over the 8kg, IIRC it weighed in at 9.2kg. Agent said absolutely nothing. Tagged my bag as gate delivery as the ATR has limited overhead space, told me to leave it at the stairs of the aircraft and grab it in Belgrade at the stairs. No charge, no issues.

BEG-FRA on a 319...I checked in online, left my gate delivery tag on...just in case, keeping up appearances you know...never went to check-in as i had my BP in passbook. Walked up to the gate, went through no issues. I did get a couple extra looks from the woman checking passports directly at my bag, but she never said anything and there were no scales around even if she had. I suspect I would've fit in the sizer just fine with my roll aboard, but there's no way my backpack would've as it was def over 4kg and kinda bulgy.

So, TL DR; no issues, I would bank on the same experience in the future as long as the bag is of a sensible size and try to avoid going to the check-in, because from what I saw in BEG there's no scales at the gates. Perfectly good experience on both flights, but the ATR JU was flying REALLY showed it's age...whereas the last one I flew with Air Swift in the Philippines looked basically brand new.