I agree with davide. I too have an '08 iS 111 (108 liters SB said at the time). I also weigh 167 lbs. The 111 has enough flotation to make slow slogging or uphauling very easy. The wider tail compared to a Futura will help with early planing, but once moving, the Futura will be closer to what you have been sailing.
My favorite sail with the board is a Maui Sails TR 7.6. (14-18 knots) Next is the 6.6 (15-22 knots) and then my 8.4 (12-16 knots). All work well on the board. If you get the iS, the Drake fins that came with the board are junk. Got to have a custom fin.
The technical aspect of the iS is more about footstraps than anything else in my opinion. They are outboard and the back strap is a little difficult to find and get into without stepping on top of the strap or sticking your foot into the water. Once in the straps, no problem, but chop hopping & tricks are probably out because of the outboard straps. Gybing is a different on the iS, but it is something that can be learned quite fast.
My issue with foot straps is a result of sailing three boards interchangeably, all with different set ups. My body is a little slow to adapt to the different strap locations when I change boards.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.