I started with a 28" hard-side Samsonite when I first started traveling and it was usually around 25kg. As I started to pack better (e.g. fill shoes with items, use space saving compression bags, fold clothes better), I was routinely packing it full and it hit the 29-30kg mark quite often.

Basically, with a 28" bag, I found the only way to keep it under 23kg was to not pack it to its full potential. So then, why even bother using a 28" bag? I went down to a 25/26" bag and am able to pack it pretty full and it comes it at 22-23 kg when fully packed. I am able to get more than enough clothes and business items in there and the bag is much easier to manage around the airport, in cars, and in a hotel room. I also do carry a small overflow bag (red oxx extra small aviator) that has come in handy when I've had to carry extra items for work.

Good luck to you on your travels, and hopefully you pick the right size bag for you and don't have a 28" sitting in your closet (as I do now) in the next few years.