If it holds the line you want, and the balance suits you then it’s fine. Unless it just looks off enough to bother you.

The #6 is a very light reel so it's not too heavy on a 7'6" glass rod. If you don't need the capacity you can increase the arbor size by rolling up a strip of thin cork sheet around it. Secure it with a wrap of electrical tape. It's lighter and cheaper than backing. To be honest with a DT 4 or WF 5 the amount of backing needed is just fine.

It's only on 7' rods that I start looking for the #5 - mostly for the aesthetics.

The #6 is 3 3/8" while the #5 is 3" and they are the same width. The weight difference is roughly a quarter of an ounce.

The #2/3/4 on the other hand is quite a bit smaller, It's 2 7/8" and also narrower. I can't see it on the 764 but it will hold a WF4.

I am a big fan of these reels also in the black Ultralite Disk version which have the option of being run silent.

definitely don't overthink and pass on the JLH - best reel Hardy made, IMO

Agree, 100%.

I use DT lines and find that a JLH one number higher than the line weight, e.g., a DT4 line needs a #5 JLH, a DT5 line needs a #6 JLH reel, etc., allowing the line and 50 yards of 20 lb Dacron backing fo fit comfortably.