Hi
In fact, specification of an Analog filter depends on application requirement. that is, if your filter does not have a large signal at its input, slew rate of the Opamp or OTA is not very critical spec. that is in most cases. to design Gm-C filters you can refer to John & Martin's book, Chap. 15. another good tutorial paper about low-voltage techiques and designing CT filters in the following:
Sh. Chatterjee, Y. Tsividis, P. Kinget, "0.5-V Analog Circuit Techniques and Their Application in OTA and Filter Design," JSSC'05.
Regards,
SAZ