Hello everyone!

I recently flew my extra 300s for the first time running a K&B .45 sportster (keep in mind the engine is a few years old) swinging an 11 x 7 prop.
Plane seems under-powered and the engine shows some reliability issues....
I have a brand new Tower hobbies .75 with a bisson pitts exhaust as well as a brand new OS .46 LA.....
I'm trying to decide which engine would give this plane the power it needs....
I know the .75 would have a higher fuel consumption and the stock 8 oz tank might not cut it but at the same time i'm worried that after breaking in the OS i might be dissapointed with the power delivered.
Just trying to see if anyone has had experience with this model and these engines.
Thanks,

Dave