You are correct when you say I am using the boom too low on the formula in light winds because on the downwind leg (broad reaching very broad) I feel very uncomfortable because I cant get the backfoot pulled under me and I cant push the front away enough to keep the board broad and be comfortable, so I will raise the boom as you say around eye level. I have tried it, and it is uncomfortable because you cant really cop out when u r knackered and get in the harness lines too early. The other thing is I generally hate long harness lines, but I will persevere, because unanimously all the threads agree a formula rig boom should be around eye level.
Regarding the rigs - I only have a 10.5 as my max sail - due to lack of finance - As u know 11.5 means new mast new sail and another boom really - so as you say I will have to accept I am under powered. The thing is I am comparing with lighter Guys with 10.'s so i guess the physics laws rule. You have made my mind up anyway, If I replace the rig it will be 11.0 and the next change is 9.0.
I can afford them new but I guess next year used versions will be cheaper. What do u thing of the new NP RS Racing?