I've only done some very preliminary reading of the rules and the options are a bit baffling to a non wargamer.
There seem to be lots of tradeoffs, so longer barrels give greater range and possibly accuracy, but take longer to load so firing times would be slower. Shorter barrels might decrease loading times, but at the expense of range/accuracy. Size/quantity of shot might also be a factor. If you put a really small ball in a big barrel then I guess that won't be as accurate. But I don't have any figures or trials which provide any data. If a long barrel only gives a tiny improvement then it may not be worth the reduction in speed, but if the short barrel is so inaccurate that I would be blasting away and not actually hitting anything then I may as well go back to using sticks.
Then there are such things as anti-rusting developments on different parts, special sights, different pans to protect the eyes or keep powder from getting wet.
All of these seem to add much cost and complexity.
And finally whatever the ideal musket is (for England), it needs the right tactics to use it. So if I am going to have my redcoats stand in line and fire it is pointless them firing at long range if the muskets have short barrels or are inaccurate, similarly if long range fire is ineffective in 1700 anyway then perhaps I should be looking at a short-mid range musket and hold fire until close range when I will actually do damage and not just run down my powder.
I have an open mind about all these things.
There are only 2 things I have decided (unless I am talked out of them):
1. flintlocks seem to be vastly superior to matchlocks, so I am going to use flintlocks.
2. I quite like the name Victory Musket (Model 1714) as that would remind the men armed with it that they won a war without using it, so if they mess the next one up they can't blame the muskets.