If I go by this method, what power can I expect on qrp/5 watts? From what I understand, I should get full power out of the tbolt with 5 watts.
I doubt you'll get "full power" with 5W drive, but should be able to with ~10W drive. At least, that's my experience with an original unmodified one as I bought back in 1973 (that was a "one owner" unit and the original owner did nothing to it but use it).
"Full power" was 1 kW DC input power, or ~650W output. The tube are good for much more than that, but not with 2200V on them.