I would keep the 300WATT PURE SINE WAVE model. this will also be big enough to run your HOME ENTERTAINMENT items like the HDTV and the DVD player. Glad to see you have the PURE SINE MODEL...
I went with the 150WATT MODEL and found out how nice it was to have so went to the 300watt model later and final went to a 600WATT PSW model. This is something you keep finding a use for haha...
If you only need to use the inverter for 150WATTS it won't draw any more power than 150WATTS even though you have the 600WATT model Inverter... My 300WATT model would just barely run my 120VAC coffee grinder. It was hit or miss getting it grind my coffee beans without tripping off. That was the last straw for me haha. Changed to the bigger unit.
Roy Ken