I'm studying both History and History of Art here in France and you may not be surprized by the fact that History is more about economics and politics matters (since I'm not yet specialized in a particular era). History of art, however, is a surprisingly good source of knowledge about war matters. I've found during my researchs lots of interesting books and other stuff about history of war ("Le livre des armes et armures" from Christian-H Tavard for the ones who can understand french, is a must-have) and I'm more or less comfortable with the subject regarding the medieval West.
There's a lot of misbeliefs on this particular era (and I probably still have many), but I can assure you that these armours are not as annoying/uncomfortable as it seems, and leather amor can impact a lot more mobility than mail armor, simply because rigidity is more annoying than weight in the short run. Furthermore, Geralt is nevery fully covered with mail or even plates, it's just minor (but yet very effective) defenses against most common medieval weapons, allowing Geralt to do a few mistakes against human opponents (not monsters that's for sure) without carrying pounds of armor.
Based on what I know, the most useful thing Gerald could wear with little but no discomfort is a "cervelière", don't know if there is an English word for that but an open helmet covering only the upper part of the head. (or maybe a small breastplate like the Roman Camillan Hastati) It's terribly unsexy for our Great Knight of Lyria-Rivia but hey, caution first !
In short, I think that these armors are all but out of context for Geralt use, and I admire CDPR work as always.
Two things rapidly found on the web can show what I'm thinking ;
https://www.youtube.com/watch?feature=player_detailpage&v=5hlIUrd7d1Q#t=6
http://www.metmuseum.org/toah/hd/aams/hd_aams.htm#only_b
the first shows that even with one of the most efficient (and uncomfortable) armor we could imagine, we can still have a quite good freedom of movement, so I let you imagine what a Witcher can do wearing lighter armors.
The second one is just a summary of some misbeliefs, in English of course. You probably know all this or don't care at all, the .4 is the one that I want to point out, it illustrates well what I think about these armors being pointless for our Witcher, always taking the extreme argument of wearing full plate armor.
I hope I haven't made too many mistakes in this post, usually I am discouraged before writing everything I wanted to say. Reading is much easier.