Speaker choice for 50w push-pull tube integrated

I have a Graaf GM50 tube integrated paired with relatively inefficient Sonus Faber Cremona Auditors (88db, 4ohm), and may begin to look for a more full-range speaker with an efficiency rating better matched to the amp (maybe 90db, 8ohm). My budget is $6,000 or less--used would be fine.

Does anyone have a suggestion for speakers that would be a synergistic match with the 50w push-pull Graaf? My system fires across the short dimension of an 11" x 30" room.

Thanks in advance for your input.