If possible I'll go with the exp/imp option, schema by schema which will allow you to be importing some schemas in 10g while still exporting other in 8i

We just did exactly that with a 200 Gig database, unfortunatelly one of the schemas was 190 Gig in size.

Total exp time: 6 hours
Total imp time: 7 hours

What we did was to exp/compress and to uncompress/imp on the fly in order to save disk space and specially network traffic during FTP.

During Import set target database in noarchivelog mode