A P-120 is plenty of power for the SBB at any weight. mine checks in at around 21 Lbs. dry, and has great performance.

As originally designed and kitted, the Bandit was powered by a JPX propane turbine that only made around 13 Lbs. of blow.

A P-120 has twice the thrust of the JPX.

A P-80 (If turned up), will make an honest 20 lbs, so you will have plenty of power. My first Bandit in 1999 had a 17 lb. Ram 750 (original version that had an oil tank..S/N 43), and was very fast...

Now, most of them are in the P-120 class and some are even higher. I know of one individual, who's name I won't mention, that has a P-180 in his composite Super Bandit.
It must be a virtual rocket! Short, very fast flights! My P-180 is very thirsty, so the internal fuel in a standard Susper Bandit (3.6 liters) must be consumed in short order.

Minch,
A SBB with a P-70 is a perfect combination. Build it as light as possible, without sacraficing strength, bolt in a P-70, and you will have lightweight combination that will give you very good flight times, and will be a ton of fun.

Which engine are you using?

Harley Condra
BVM REP
JetCat REP