suggestion - Non rac database to rac database migration methodology

Currently we are migrating an non rac database to rac database.

Source:

    OS :RHEL4
    Database Version: 10g R2 32 bit
    RAC : No

Target :

    OS :RHEL5
    Database Version : 10R2 64 Bit
    RAC : 2 node ASM database

For the above migration, i have taken expdp/impdp methodology.It takes 15 hours to complete activity.(The data transfer rate from source to destination is 300KB per seconds)

Please suggest as any other methodology for this migration to reduce downtime.

Regards
Krishna

--
http://www.freelists.org/webpage/oracle-l