They are very different watches in terms of style look and feel .
I have 6497 running strong after 5 + years with No services. I have had some good and not so good A7750's just watch your date change adjustment. Look they are Two Hundred Buck watches of $5K watches , they might last ages they may not , you might want to buy new or find a rep friendly watchsmith . None of these should stop you getting a new watch should it?
Getting a chrono serviced might cost more than the cost of a new watch, I am all for keeping and fixing but you have that choice.
Finding an decent strap is much more of a requirement Rubber straps are a big dislike of mine.
TS is a pretty good dealer IMHO, not as quick as some but pretty reliable
Just Pick one