Oh yeah, force 9-10 spirits are going to be out of easy reach. Not to mention that when binding said spirits (remember, you can only have one unbound spirit at any time), they get to roll twice their force (20 dice).
You're looking at a nice 5k ny price for an average of 12 physical drain to resist with your 8 dice. That means you take an average of 10 physical. You've only got 10 boxes, and if you go unconscious (As you would from losing your entire physical track), the spirit goes free. When a force 10 spirit goes free, it has a fair chance to become a free spirit, who can then do whatever it wants, and it's got a nice little summoner who is unconscious at its feet.
Also, remember that spirits get edge equal to their force, that they CAN use to resist summoning and binding, and that more powerful spirits have more individuality. A force 10 spirit may not take kindly to a random guy summoning it, much less trying to bind it. (And once it becomes a free spirit, it may just squish your overflow track.)
Summoning that powerful of a spirit isn't really advisable, binding it even less so. It's likely to draw GM aggro (no matter how much your gm avoids such things), unbalance your campaign, and/or get you very very dead.
EDIT: I wouldn't advise summoning/binding anything stronger than the 4-6 range. 6 is kinda pushing it usually. Remember that the drain you take is independant of your summoning/binding skill. You have to resist twice the hits of the spirit when it rolls force x 2 for binding. For a force 6 spirit, it'll get an average of 4 hits, so that's an average of 8 drain to resist. You'll take more than half of your physical condition in drain damage (on average) any time you try to bind one!