the toroids size?

I have now finished rolling the secondary for my coil, and I setteled
for a polypropylene former, 7 inches dia, with 900 turns of wire, 0.75
mm dia. That`s in between 20 and 21 AWG. 19.4 ohms DCR
Aspect ratio is 1:4,1 .
Tesla coil cad predicts 31.3 mH, and I have measured 31.4mH
Self cap: 13.54, I don`t know how to measure picofarads.
The resulting resonant frequency is approx. 244 kHz and the quarter
wawelength resonant frequency is 147 kHz. This is met with a topload of
23.73 pF.

Question is:

Should I proceed to make a 1/4 wawe resonator out of this coil, ie.
stick with the 23 pF, or is it ok to go higher, like 30pF for example?

I admit to designing this coil, at least to some extent, according to
how it looks. Does it look harmonic?  I think that a toroid slightly
bigger in diametre than the secondary coil itself, and slightly smaller
in OD, than the primary, (which in turn has a diametre equal to the sec.
coil hight.) makes the whole unit look good. 

Nice, fat toroid.

Such a toroid would be 8" Dia. allu. duct. 20" center to center dia.
and be 31.15 pF. Allow more primary turns in use, all else equal.

I will, in due time, have 3 kVA to pour into the thing.

Cheers, Finn ( getting closer to sparking time )