I bought some Van Damme XLR connecting cables. They do the job OK but I was a bit disappointed by how thin the actual conducting cores were. The cables look chunky but most of that is insulating material. Looking at eBay listings for 4mm Van Damme speaker cable it looks like they follow the same pattern.
The thickest multi strand copper cables that I've been able to find so far has been 762 strand which costs £1.08 per mono metre in 100 metre rolls, and a bit more per metre if you buy shorter lengths.
I would have thought that small bookshelf speakers would benefit more from thick cables than huge speakers due to the bookshelfs tending to be be less efficient than large speakers, and therefore drawing more power for a given volume.
Speaker cables are one of those things that you should try yourself if you're interested. Some people feel that they are important, other people feel that they are unimportant. It's possible that your old Gale cables might sound as good as anything else in your system. It's also possible that you might prefer something else.