recommend rear 7.1 speakers??

[MATTYBLU2]

hi, i have a 5.1 cambridge soundworks bewton series setup now and will be upgrading soon to a 7.1 sound system. i want to add 2 more speakers to the rear for the 7.1 system.

what kind on speakers are good for the rear (not surround speakers) channels behind you? can i get the same speakers i have for my surrounds or do i need straight firing speakers? my surrounds are half moon (model S300) with 3 angled mid ranges firing front, center and back, and a tweeter in them each.

any advise or opinions on which ones to use? is it ambient sound that comes out of them? is it very noticable with a 7.1 track? wondering if it is worth the upgrade as well.

thanks for your time