The weight pouches on my Scubapro Knighthawk can take about 10 lbs / 5 kg each. I imagine the weight pouches on the BCD you describe are the same. The Knighthawk also has trim pockets which can take another 4 lbs / 2 kg or so, bringing the grand total up to roughly 30 lbs.
I use a mixture of soft and hard weight. In general, I prefer the soft weights (seems like they can be squished a little more conveniently into the shape of the pouch). However, I have a bunch of 2 lb fishing weights which are very convenient for adjusting trim, or making last minute adjustments, or lending out to buddies.
Are you diving a steel tank? You could probably get 2 - 3 kg off your belt by switching from an 80 AL to an 80 steel. That might make the integrated pouches a little closer to sufficing for you...
- steve