12' L from seva has better performance than 14 MK 7L (12' L has a little more range and way better damage)
but they are (just my opinion here) a little worst than 16'L Mk2 (in barrel by barrel performance). the problem here lays in that Colorado/Tenny's guns have only 8 rounds for 4 R slots, while 12'Ls have 12 rounds, wich gives final advantage against those

the best gain for PBB is to skip all the crappy BB1 (really BC Atlanta/Guam with those 45degree-no-range 12' and BB Nevada with 0-turning-speed-and-poor-overheat are no more than bonus stage for enemys. Premodels are decent BB1 but overpowered by anything from BB2 on)

the other gain is to use it till BB3 (sometimes used till BB4) but i have to say that Colorado is a very fun ship to command (also tenny remodel, but Colorado has better OH speed and 1 extra bind of ammo for 16 duals MK2 and triples MK3)

if u alredy buyed it USE IT, but if u alredy passed BB1 stage and reached lvl 70 Colorado/Tenny(remod) just stick with that BB2 u have and save olives for vets and experts

:::::::: about the angles ::::::::::::::

14' MK7 has 30 degree angle
Seva's 12' has same 30 degree
16' MK2 has 40 degree angle

for ships with 30 degree u should NOT carry AP round, they only work from 30º on, so u just can shoot AP round efectively at max angle only, if u go down to 29º you will be hitting Belt, wich noone will ever be puting any armor over 0.2 to 0.5. So if u came up against a UK armored BB you should let him come till angle 29 and use that angle as "max angle" to shoot against him