Interesting this conversation on the relative rarities of the 1843 and 56 pennies. While not a serious or scientific study, some idea of relative rarity can be derived from the LCA sales over the last 20 years.
1843 sold total 44 coins, 19 absent colon and 25 colon present of which 5 are DFF.
1856 sold total 65 coins, of which 46 plain trident and 19 ornamental trident.
This would suggest that 1843 is the rarer date, though of the varieties 1843 no colon and 1856 OT are found in similar numbers. The total sample of 109 coins is likely to give a reasonable degree of accuracy, but not absolute- is there a statistician in the house?
The prices paid for these latter coins, even in VG or corroded, tends to hover around £100.
Jerry