Would they go well? Technically yes. They use exactly the same drivers as the R90HD's, so panning effects front to back and left to right will voice extremely well, and surround music will sound excellent too. (A good example is a recent purchase of two classical Bluray Audios (Naxos' Copland Rodeo and Rachmaninov Piano Concertos 2&3) which sound truly stunning and give evidence of how accomplished the Radius speakers are when fed well).
However they are very different speakers and will affect the overall balance and feel of your system. I originally had the Radius One HD for the front three channels, which was essentially two R90HD's and an R180HD in one cabinet, not too dissimilar to your current system. I traded up to the R270HD for left and right with R250HD centre, so my comments are based on this change.
The R90HD's are lightning fast, but can be a little lean in the midrange, even with subwoofer sharing the frequency range. The R270HD has a much more fullsome weighty midrange and upper bass. The upper bass is very impressive for such compact floorstanders. They're not perfect though. They have strengths the R90HD's don't have, but they trade in some of their strengths too.
Downsides;
The R270HD's are much more finicky with speaker placement. The closest to the back wall I could get them without the bass becoming boomy was 450mm, and that's bunging the rear ports slightly too. They'd prefer even more free space, but the room doesn't allow. There is a smidgen of cabinet resonance that's not there on the R90HD's; it's only noticeable with certain frequencies. Like the rest of the range, I find them very 'directional' speakers, so don't spread the soundstage very wide. The upside of that of course is that steering effects are very accurately placed.
Advantages;
If you choose to play any 2 channel sources in 'pure direct', they are much more capable of course than the R90HD's on their own. I particularly find this with two channel TV sources, although the small soundstage / directional behaviour caveat applies here too. And the midrange can sound drop-dead gorgeous if fed the right stuff. Vocals really sound lovely; Corinne Bailey Rae, Lianne La Havas, Mayra Andrade, the Staves all sound as wonderful as their honeyed voices should.
So on balance, I'm pleased I made the trade-up. They make my whole system more flexible, and for the more musical movie soundtracks (such as 'Invincible' which has a beautiful array of 70's classics), it's a far more accomplished performance. Just make sure your room can make sufficient space for them and don't pay more than £400!
(PS, there are pretty good clearance offers at Peter Tyson at the mo)