I don't know how familiar you are with fencing and sword fighting in general, but having trained kendo (modernized form of japanese swordsmanship) for a couple of years I think I can safely assume to have a feel for what is and what isn't realistic concerning a sword fight.
In my opinion, parrying a correct thrust or swing from your opponent is far easier than actually manage to connect a correct thrust or swing against him. Making some of the close combat talents in Dark Heresy somewhat strange. You can easily buy swift attack and lightning attack, giving you more attacks in a single round, but there is only ONE way to increase the number of parries you can do, and that is by buying the wall of steel talent, and that will only let you parry ONE extra time during a combat. Making you pretty vulnerable against opponents who have lightning attack since they can stab at you three times while you can only parry two.
I find this to be absurd, based on my experience in how easy it is to parry a sword strike in comparison to attacking with a sword. And yes, I do know that kendo is a sport primarily and a form of martial arts secondary, but you have to remember that while certain forms of cutting and thrusting are only accepted by the judges, this emulates realism in a way since a sword has to be wielded and swung in a correct manner to actually do the maximum amount of injury to an opponent.
Desperate swings and thrusts by an untrained user are dangerous of course, but they are a far cry from the thrusts and swings of an experienced swordsman, that can easily kill the intended target in one stroke if the target is unable to defend him- or herself. This is especially true with japanese swords like the katana with the peculiar curvature of the blade. An experienced swordsman wielding a katana knows that his swings has to have a certain circular motion to them in order to achieve the fierce cutting power of the blade, while inexperienced swordsmen have a tendency to chop with a sword like it was an axe, which could do a great deal of harm, but you won't sever someones head with a katana if you use it like an axe since it is a cutting weapon, not a chopping weapon.
So while I agree that you can't base full knowledge of real swordfights on kendo alone, due to the discipline's sports-like nature, it is quite reasonable to assume that you need to wield a sword with the proper form if you want to use it as efficiently as possible, and we can assume that swordfighting and melee damage in Dark Heresy are based on as efficient blows as possible, rather than desperate swings that are more likely to maim or injure rather than kill.
So, my main intention here is to make it easier to parry several times than it already is in a sword fight/melee fight in Dark Heresy. My proposition is that characters with the swift attack and lightning attack talents can opt to not use all of their attacks during combat and instead use these unused attacks to parry several times instead. This ruling would make the game slightly more realistic, while at the same time not topple the standard rules. Wall of steel could keep it's function like usual, even if you can combine it with this sacrifice of attacks in favor of parries.
What do you think?
), and I thought I should include it just to show that im not a terra firma rooted realist all the time, and that I am perfectly able to think in over the top, adrenaline-pumping action ways as well. 
