According to the NRC, an 807 has 374 seats in standard and 40 seats in first class. A 390/0 has 370 seats in standard, and 99 seats in first class (so an 807 has more standard class seats than a 390/0), so for the vast majority of passengers, there are actually more seats in standard on an 807 (it's also worth noting that 143m of an 807 is standard class, with 144m of a 390/0 being standard class).
If/when the planned increase to 2tph on Liverpool happens, it will be run by an 807 (for the one that stops at South Parkway, i.e. the current regular path), and a 390 (on a new path, stopping at Runcorn, Lichfield T.V. and Tamworth). This gives a total capacity of 744 standard class seats per hour, and 139 first class seats per hour, which is, of course, a rather major increase in capacity, and will certainly be welcomed.