If U know U R going to change speakers why buy the amp now?
Traditional wisdom is to get the source and speakers right and then worry about synergestic amplification and cabling.
Buying too much amp has its drawbacks just like buying too little (or too warm for the rest of the system, or not warm enough, or etc. etc. etc.).
Other thing, if you are going big tube power you need to listen to the ASL Hurricane and Rogues and the big CJ. The more cost effective options are sometimes also the best sounding options, depending on your system and preferences.