Urbs, again your question is one where there is no wrong answer. The Rachael with 6 WPC will drive any Omega speaker to more than adequate volume with some headroom to spare. The question should be is the additional cost worth it to you...sounds like you're on a budget. Do a little reading of impressions of both drivers at the Audio circle forums that can be accessed from Omegas' website. Also read what Louis says. I chose Alincos but it turns out mine are DIY versions Louis once sold not the same as those that would be in your monitors. I'm going to send you a PM with something you may want to consider. Mark.
http://omegaloudspeakers.com/omegaoemdrivers.html Alnico Magnets
When I first heard the Alnico (magnet) sound in a driver, I knew it was for me. Now some upper-end Omega single-driver loudspeakers use Alnico magnets in their drivers.
Alnico is an acronym referring to alloys which are composed primarily of aluminum (symbol Al), nickel (symbol Ni) and cobalt (symbol Co), hence al-ni-co. For comparisons sake, 99% of dynamic drivers used in home audio utilize ferrite magnets.
For a speaker designer, Alnico drivers are MUCH more expensive compared to their ferrite counterparts. But there is no question in my mind, Omega's proprietary Alnico drivers produce the sound and tone I strive for, so they are now used exclusively in some of my upper-end models.
Compared to ferrite magnet counterparts, the sound produced by Omega Alnico drivers:
Is better balanced and more linear across the frequency spectrum.
Has better texture and layering.
Offers higher resolution (especially noticeable in the mid-bass area, with instruments like standup bass and kick-drums.