The P47 is "inferior" to both F4u and P51 at typical MA altitudes. 20+kft is a whole other matter. Taking 6 or 8 guns will not change that fact.
However, consider this: One of the few things the P47 excels at at all altitudes is to burn a lot of E for one good shot opportunity - which it better hit home with, because it will not build its energy back so fast and is left wallowing. 8 guns is 33% more firepower than 6. It might very well be the difference between a killing/disabling snapshot and merely damaged paint-job on your target. Vs. many opponents you will not get a second chance. In the MA you must make your kill FAST and get out and 33% extra firepower will do more for you than a small reduction in turn radius. When the latter comes into play you are very likely to die anyway.
Finally, the weight difference between the 6 and 8 guns is negligible compared with your fuel weight, unless you are very low on fuel and don't mind it - as in a duel. So, in the DA taking 6 guns may make some sense, but in the MA, the 6/8 difference will be blended with your fuel status.
Without 8 guns, you might as well be in the better-performing F4U-1A or a P-51D.
NO NO NO. A P47 pilot will rather fly a P47 armed only with his .45 and foul language, than be caught in a P51 or F4u.