"In Kendo you often use overhead attacks with the sword"
All attacks in Kendo are lethal; which is why you charge foreward through the opponant, he's not there, you just killed him.
All attacks are full strength attacks, begining from behind the head, cutting through the target synchronised with a scream, and moving forward right foot first through the opponants space. Failing to complete that specific sequence will invalidate the cut and you score no perkies! There is no fencing, merely full cuts, stabbing (to throat and thorax) or jabbing with the reversed sword handle to throat or thorax. As you've already found out, you cant fence in full armour any way.
The best sword fighting you'll see on film is an old Bob Mitchum film called "Yacuzza". Really good.
The nearest you get to a "slashing attack" are a down ward cut to the left side of the opponants hip, twisting the blade to cut him in half at the hips, or a down ward cut to the oppoants right side, relaxing your grip and disembowling him as he runs forward.
You may always cut off his right hand, and his left too if it's above head hieght.
There are only eight targets in Kendo:
The sides and centre of the head
Throat and thorax
The Hips
The wrists.
Remember, Kendo isn't "Japanese sword fighting"; it's a Japanese sport using swords. (Nothing with "Do" on the end is Japaneese fighting, but a Japanese sport, that's a post war, post MacArthur invention)
Here's a conundrum for you - every one knows Samurai have two swords - but any Kendo master will go ballistic if he catches you practising with two Shin ai (I made of couple of short ones for friends), I've never found out why.
Ia, if you can find a teacher, is closer to what your looking for, it's best described as "the art of the quick draw"; very elegant and often done with live blades.
Remember that swords were expensive and rare, the halberd (sword on a stick, can't remember the oriental name) is an older and more common weapon, and the one Samaurai women were trained with too. Tie some long ribbons to the blade/stick join, it looks great when you're practising.