single class B zone vs multiple class C zone

[Hannah O Day]

I have both dhcp and ddns servers (BIND4.93) that run on Aix boxes.  I have
been config all reverse zones on the per class C subnet basis.  I'm now
upgrade the server to BIND8.2.3.  I want to config the reverse with only
one class B instead of many class Cs.  Could anyone tell me if this will
cause any performance issues since the updates will now happen to the
entire class B instead of class c?

Thanks!

Hannah Day