What is the consensus for the use of siege ? Bombard till it's 0%, then suicide enough of them so that the maces are at 99% ? Use more cats when they start having decent odds to give them XP ? Don't bombard, suicide and attack ?
Hmmmm, how to answer this one. The best answer is that it depends.
When attacking Ragnar, I used 2 suicide cats against a stack of horse archers that arrived a few turns into the war, and 1 on Upsalla, but other than that they simply bombarded until the maces had decent enough odds.
The main point of suicide cats is to give collateral damage to either tough units, or many units. Ragnar didn't have many tough units (he was defending with archers/swords). He also generally only had 3 defenders in each city, thus reducing the net benefit.
The other thing you must weigh up is speed. Every turn you are at war, the enemy is building/whipping units.
If you look at my log, I DoW, then bombarded for 2 turns, and attacked after the second bombardment, with odds of 73%, 70% and 99%. I got lucky I admit, but I did have a few more maces ready to attack.
The next turn a stack of 1 WE and 3 HA appeared, so I used 2 cats at 12% & 48% to make sure they wouldn't be attacking me. The flank attack of the HA's is particularly annoying. The maces then cleaned them up the next turn.
When I attacked Upsalla, I took 4 cats, bombarded for 2 turns, except for 1 suicide cat against his promoted, fortified, in a walled city, axe as the combat odds for my mace were only ~50%.
Anyway, the point I am trying to make, is that there are lots of factors, and it can be hard to judge.
At the start of wars, when taking big important cities early can swing things, I look for odds > 70%. Once the war is effectively won (which I believe it is with Ragnar), then you can take more time to bombard defenses down to 0, and use siege to ensure that I get odds > 90%.
Make sure you only suicide the turn you want to attack with the main forces. There is no point letting his units heal the collateral damage.
The appearance of our super-medic will also be a factor, as you can roll a stack onto the next city immediately and heal the maces while the cats bombard.