Low performance climbs

When flying a plane that doesn't have a lot of climbing power, is it
quicker to get to your destination if you climb at a slower rate, but
faster speed? Or is it quicker if you climb faster to your altitude?

For example, say I took off at sea level and want to cruise at 6,500.
I don't need to be that high for terrain clearance for some time. In
a fixed pitch plane, I could climb at Vy to get to the altitude using
full throttle, but this gives lesser engine cooling. If I climb at a
speed greater than Vy, I'll need to reduce the throttle more (fixed
pitch) to keep RPMs in range. When I do this, it seems like it'll
take forever to get to the altitude, however.