Hello!
I have a MVVS 1.50 glowengine in my SIG CAP 231 EX and use either a 17x8 APC or Better yet a 18x8 Menz ( wood prop) .
The rpm with the Menz 18x8 is 7800r/m on 5% nitro and 15% Motul "Micro" all-syntetic oil.
It could hover and then accerlerate staight up!
Never, never use lead for balance if you could avoid it!!!!!
Planes got to be light to fly well!!!!
Just balance you plane by moving your servos and batteries! This takes a little more time then just attaching lead....but it makes the plane much nicer to fly!
And belive me..... the 500cc (16oz ) is enough a 24 oz tank will make the plane to heavy which will make the plane a not so good performer.......

Regards
Jan K
Sweden
In this hobby for 27 years