i have that nashbar carbon fork on 2 steels. Gotta say I like the fork, looks nice, ride is great without being mushy.
Improvement over original stock steel fork? Dependez on the steel fork...
One frame came without a fork... Torelli Corsa Strada frame - Columbus Brain tubing. Bike rides as thought the fork was matched to it, nice...
Other was a Marin Treviso - Columbus Neuron - super tube set matched to a 'anchor' of a steel fork, rode like ****! - the nashbar (same as thread, but this was the 1" threadless model, same fork otherwise) made all the difference in the way the Neuron tubeset now rides - an absolutely marvelous blend! Out of 10 road bikes, the Treviso now sits at number 2 FAV behind my Spec Roubaix.