I agree with all of the above on the Regas being a great match and extremely enjoyable. I also agree, however, that the R3s are a bit laid back and musical, all be it a bit euphonic and a bit "loose and bloated". Not a bad thing in a synergistic system, but the Brio R raises the bar with control of the music and additional extension in the bass. The R5 tightens things up a bit, but still exhibits Rega speaker qualities.
The new Brio can now take advantage of a tighter, more resolute speaker than ever before. There are few floor stand speakers in the price range you mention that are musical and will match up well with Rega.
I just heard Neat Acoustics Motive 2 small floor stander on a both Rega and naim gear and was quite impressed. Much of the great qualities of the Rega speaker, but with improvements in all the weak areas. Much better rhythm, timing, dynamics, and extension. I think the price is not far off the Rega R5.
Just a thought if you can find them.