I don't know how much experience you have so these coments may not apply. If so Please ignore them. I have found that modern sails (and probably older ones) can behave very differently depending on tuninng (outhall and downhall settings) and mast and boom combination so varying these may help in how they pump and behave in different conditions. Unless you are very experienced it is more likely your settings or technique which need adjustment than the 8.5 overdrive not working.
I often use a North F9 8.4m sail (simillar class to overdrive) on my phantom 320. with my skill and weight, I have found it very good in strong winds up to 22 or so knots, and still powerful in under ten knots and nonplaining conditions. But no matter how good a sail is it is hard to beat and extra square meter of canvass for power. My 9.5m starbord sail always seems more powerfull as long as it is not overpowered.
You may be very disapointed if you think a choice of sail is going to solve all your problems. As long as you are using a reputable brand, the easisest and surest way to make sure you have more or less power is to go up or down in sail size.