Next step: tube pre or tube power amp?

I own a Rotel pre/pro RSP-985 SS preamp and a matching Rotel 120 watt power amp. If I wanted to move into tubes, would I get better mileage out of a tube pre or tube power amp?

I love the convenience of the rotel preamp (remote, built in DACS etc) but I understand that a tube pre will have more impact than just a tube power amp. Is this correct?

Also, my speakers are 91db efficient. What wattage tube power amp would I need to drive them to medium/loud levels?

thanks

Steve