I don't recall anyone coming up with a combat used 10 rocket load out yet, despite lots of looking.
I think it comes down to what they did do operationally vs what they could have done.
Not my call of course 
I don't have a copy of it myself, I think someone in one of the numerous pervious threads did provide documentation of larger DTs being used operationaly for long range escort missions in addition to large drop tanks or bombs + 6-rocket combos being used in long-range ground support missions over the Pacific with mustangs.
Specificly for just 10-rockets, you may have a valid point, but I think some from the Korea era were produced... and this is where the discussion turns into a debate, as some points can be made while referencing the current P-47 and it's ability to currently carry loadouts that it also mostly (if not exclusively) utilised during Korea.
So, while trying to avoid that subject it still raises another question, why then choose to err on one side with this aircraft (and only 4-more rockets) and not the others?
Also, when looking at the way these fire control systems were installed (the bare-bones) or shipped/supplied to units as a post-production field kit for installation, they all came with 10-rocket capability once upgrading from tubes (which btw the earliest P51-Ds did have and would ALSO be a valid request as I also recall its use was documented) or you simply didn't have the fire control system necessary.
I thought maybe HTCs got creative here, they've modeled a mustang with the old 3-tube bazooka firing system but shooting the new rockets (so 6 rocket maximum capability, + ord), BUT that would mean that it was then field modified to shoot 5" rockets instead, which could make sence except it blatantly goes against their use of field-modifications (where's our beer-keg drop tanks or up engined 190s?). See, 5" rockets needed these mounts (one on the rear and one about midway) that are specificly for them... like many creative ground crews, give them enough raw material and the right tools and they can make it themselves... but they didn't do this for the most part in WWII. They were shipped a kit that included 10 front and back 5"-rocket mounts AND a new firing system/ontroller with a maximum/stanard capacity of 10 rockets (or 6 + ord).
Maybe most fundamental reasoning to my arguement for 10-rockets is this: To limit them to only 6, specificly without any other ordnance loaded, is a blatant field modification and non-standard USAAF practice. Can we document a mission flown with only 6 and nothing else on the wings?....
So yeah, want to open that can of "field modifications are tollerable within limits"-worms instead?
