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It is obvious that when the valve is closed (240 deg lobe example) it has more clearance than the partially open example of the 280 deg lobe.
You have to remember though that the 240 deg cam has much less time (degrees) to open a lot more the valve (2 mm) which makes it highly probable that it will have much more aggressive ramps.
If we make a rough calculation, one opens 0.039 mm/deg and the other 0.054 mm/deg of average opening (and closing) rates. Its rather obvious which may have more aggressive lobes...
Increase lift only if your engines needs it. Besides clearance, higher lift raises the risk of valve float as the lobe it is actually "shooting" the valve towards the combustion chamber and piston with the more aggressive ramps. To offset that, you will need stiffer springs which will robbing you power through parasitic losses at all engines speeds below the max power rpm.
I am still assuming that we are discussing a street legal sports car that it will see daily driving duty as well. Pure race engines is a different story...
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