The only problem with the RA6/8Ms is that being passive, you need to get hold of a decent amp to hook up to them, whereas the MSP5 and M1 Active works straight out of the box.
I've had my MSP5s for about a month and a half now and I have to say I love 'em. As with anything that was based around the NS10 sound though, there is a 'curve' to their response that needs understanding. Now Ott's back, he might correct me, but I think that Yamaha designed them to have a slightly pronounced mid-range response, as the Fletcher-Munson range is the fiddliest to mix well (and the most painful to listeners if you cock it up). From what I've read, the M1 Actives sound 'better', but to be honest I like my monitors to point out where I'm going wrong, not lull me into a false sense of security.
At the end of the day, if you can take a CD of something you think is mixed well, and a CD with some of the stuff you've been working on along to a shop and A/B the monitors you want to try against each other, you'll be able to make the most informed decision.
(I badgered Turnkey into A/Bing the MSP5/Alesis M1/Genelec 1029A/Event TR8s against each other with Shpongle and one of mine as reference material, then found a pair of MSP5s on eBay for £180... cheeky little sod that I am

)
As an aside, I've been told that the production quality of the stuff I've done since acquiring the Yammies is a significant notch above what I wa doing before, so I'm a happy camper.
J.