F16 spi, as your mast is the same length as the F16's and your 5.20 mtr hull length is closer to the 5.00 mtr long F16's then the 5.52 mtr long F18's. In effect the F16 spi triangle will fit alot better in you pole/mast/sidestay triangle then the F18 spi would. Less danger of bending the top of your mast or introducing alot of leehelm (long spi pole) to your boat.

Wouter