looking at new boards and just getting my facts right
the modern free ride boards around 70cm wide 120 odd lts should be able to get up and plane easy but dose the extra width mean they get out of control easy in higher wind?
boards I have in mind are starboard carve iq or jp excite hopefully still quite quick but still versitile
combination of a few things such as your weight, capability, sail size, fins, wind strength, water state etc, but on the whole either of those boards you mention at 70cm should be fine up to 25kts and potentially beyond for the average sailor of average weight etc with the appropriate kit.
I sometimes ride a 70cm wide board in 25kts plus and the major control issue I notice is rough seas or cross chop more than the outright wind strength. All things being equal a narrower board would be more comfortable and in control in those sorts of conditions. So the answer is to buy more boards 
As under fin said.
boards like the excite can be used in stronger winds by putting a smaller rig and fin on them to redcue the tail walking. but it gets to a point after 25 knots where the chop bounces the board too much
When it catchs the wind underneath it can lead to some spectacular crashes.
That being said if you can find a nice flat piece of water like the pit you wont have too many issues in 25 knots.
"horses for courses " where you sail and how much you weigh, it's not the width that gets you on the plane it's the rocker and when on the plane its the fin that keeps you planning, the width allows you to carry bigger sails for shorter length boards, the wider the board the bigger the fin, it even gets to the stage where the bigger you go the slower you go for e,g formula sailing, the main board i use is 500 wide, with a 30cm fin and a 6.2 N/PRS sail i will get planning quicker and plain through the lulls better than a another sailor the same weight and the same fin & sail on board that's about 650 to 700 wide
