Which medieval or renaissance fencing or European martial art treatise (or treatises) has the most realistic illustrations? I read somewhere that one treatise in particular was especially accurate in anatomy and other details, so the article (or post) was giving greater weight to the blade-to-height ratio in that particular treatise. I can't locate the statement. Apart from that I'm generally interested in which manuals may be more mathematically precise in the artwork and less visually creative with shape and proportion.
Actually the comment might have been in a clothing or footwear explanation. Either way I'm looking for accurate visual renderings of swordsmen, their weapons, and wardrobe.

I don't think anyone has actually done extensive measurements (if they have, I'd like to know about it!), and real people and swords vary in proportion anyway, so you may get somewhat subjective oppinions.
In my uninformed opinion, probably the best is Albrecht Dürer's wrestling text and his incomplete fechtbuch - the guy was, after all, one of the most famous northern-european renaissance artists as well as possibly being an amateur martial artist. The top professional artists of that period prided themselves on getting proportions, geometry and anatomical detail exactly right, to the point that some artists illegally exhumed and dissected fresh corpses to learn anatomy. Next (very close behind), tied for second place, I would put Joachim Meyer's fechtbuch with its elegant, realistic and highly information-dense woodcuts, and the fechtbucher commisioned by Paulus Hector Mair - he embezzled enough money in his civil-servant position to hire a really top-notch illustrator to do the lavish and realistic illustrations (and to get himself hung when he was found out). Fiore de Liberi's works are much more simply illustrated (apparently by himself!), but the figures in his illustrations generally give the general impression of being reasonably realistically proportioned, and (if I remember correctly) don't include any of the very weird contortions (particularly of arms and wrists) seen in many of the german fechtbucher - Even in Talhoffer's manuscripts, (which are possibly some of the "best of the rest", in my opinion. Possibly the fact that de Liberi must have known very well how the human body moves (and can't move) and how long limbs generally are through his fencing and wrestling, and did his own drawings rather than contracting them out to a (possibly less knowledgeable) illustrator accounts for this.

Others will probably disagree on one or more, or draw attention to books and manuscripts which I missed.

Edit: some of the fencing manuals from the bolognese school have very good illustrations, but I know very little about that system, so didn't immediately think of these.

Edit-edit: rereading your question, I see that you ask about dress and details of weapons. Interestingly, this doesn't change my answer, with the possible exception of Fiore, because of the allegorical nature of some of his illustrations, and his crown/garter symbol system. Talhoffer does have several detailed illustrations of weapons on their own, and even their construction in some cases (the pollaxe comes to mind particularly).

Gérard Thibault's Academie de l'Espée is one of the most elaborate manuals ever presented, and is quite mathematical in its focus upon geometry as it relates to sword play. In the link below, I believe you can download images from the manual on the right side of the page. It appears there is no translation of Thibault publically available yet.

http://www.wiktenauer.com/wiki/Academie_de_l%...%27Anvers)

I seem to remember seeing an English language book on Thibault a long time ago, but I forget the details unfortunately, and I know nothing about his system. I wouldn't have thought to include him for the same reason that I omitted Capoferro (whose book is very well illustrated), and his contemporaries - I tend to think of the renaissance as more or less over by around 1600 AD, after which you'd be in the baroque or enlightenment period- what is meant by "the renaissance" seems vary quite a bit depending on what historical field you are working in. (Meyer (c.1570) just makes it in, in part because he belongs to the Lichtenauer tradition).