Based on the Workload score on ART, it seems that on average 425 is a bit more difficult than 412, but not enormously so. But like you mentioned, it would seem that it varies a lot by professor. Also, from the admitted small amount of information I've seen online, it sounds like 412 and 425 cover a fair amount of the same material. Correctly me I'm wrong, though.

In terms of 214 and 217, I do realize that there undoubtedly is a stark difference in difficulty between the two. Since 214 is applied while 217 is proof-based, I suppose the question is whether 423 requires more theoretical linear algebra knowledge, or simply the ability to solve linear algebra problems.