All new HW45's .177 or .22 have the dual power option and tru glo sights. If you go down the 2nd hand route don't get the old iron sighted models - the tru glo sights make shooting far more enjoyable in my opinion. I have a .22 and never use low power mode. Can't really think why I'd want to, it's not much harder cocking for full power anyway. My .22 is running at 5.2ft/lb with hobbies, and 5.4ft/lb on superdomes according to my F1 chrono.
I wanted a .177 when I bought mine new 3 months ago, but shop only had .22 in stock. I have not regretted it at all. .22 is easier to cock - as spring is not so powerful, and also shoots smoother, with less recoil. But.....either is a fine piece of engineering, and in my opinion the finest spring pistol you can buy.
If you can stretch to it go for the silver star or black star - the luxury grips make the shooting experience far more enjoyable. I find the standard '45 leaves my middle finger sore after 100 shots or so. Good luck, and enjoy whichever you go for.
All the best
Mark
Laminate stock HW100KT .177, HW100KT .22, HW95K luxus .22, BSA Meteor Mk3 .22, SMK Mod 12 .177, MAS 0.07 .177 BB CO2, Gamo P-23 CO2