If ye be wonderin' how ye should upgrade yer Market and House o' Navigation so's yer total galleon capacity is at its highest, ye came to th' right place matey. Follow the simple course charted out here, and ye'll have the best cargo fleet possible for the fewest number o' upgrades. Mind ye, this ain't about lowerin' the upgrades ye have t' do, it's about gettin' the most capacity out o' yer fleet with the upgrades ye do make by choosin' the upgrades that keep y' in the sweetspot -- gettin' more bang fer yer buccaneer as it were.
1. Build yer Market to level 9, where ye'll 'ave 10 galleons.
2. Build yer House o' Nav to level 1.
3. Upgrade Market to level 11 -- level 10 doesn't add a galleon, but after that yer number o' galleons'll match the level of yer Market.
4. From 'ere on out, ye simply upgrade yer House o' Navigation once for every Market upgrade.
The port ye be makin' for here, is to stay as close as ye can to the line that passes through the points:
|House o' Nav||0||1||2||3||4||5||6||7||8||9||10|
Now if time be yer main concern, 'tis better that ye get yer Market t' level 9, then upgrade y'r Navigation twice for every Market upgrade, on account 'o Navigation bein' a quicker build than Market. I must admit though, I be sailin' fogbound on the 2 to 1 ratio, on account o' th' fact that I've scouted nigh but a couple o' the build times fer the two buildings in question. And, as it stands, their build times be known to change, addin' to th' difficulty o' makin' a steadfast reckonin' in this regard.
As to th' question o' whether ye be better off with more galleons or higher payload given that ye occasionally be using a galleon or two fer tradin' sketches: first add to th' number o' yer galleons, then increase their capacity. As long as ye be near the optimal Market level/Navigation level line (either 11/1, 12/2, 13/3, etc -- or 11/2, 12/4, 13/6, etc) ye will come out smellin' sweeter than a Barb'ry comfort girl.