32-bit to 64-bit migration options

I'm planning a migration for a customer with a PostgreSQL 8.4 database cluster running CentOS 4.8 32-bit.  The target platform is CentOS 6.2 64-bit and will be running PostgreSQL 8.4 (our application delivers and supports 8.4, don't bother bringing up 9.x).  If this were a small database cluster I wouldn't worry about it however the 8.4 database cluster is about 900 GB right now.  The documented and proper way to move this data is via a dump-restore however I'm not sure my customer wants days or potentially weeks of downtime so I'm searching for options.

Option 1: dump-restore

I've performed a handful of these for other customers and even the 100 GB database cluster using the network transfer method "pg_dumpall | ssh target -c 'cat - | psql postgres'" can be slow as in 8+ hours.

Option 2: Slony-I

Is Slony-I an alternative when moving data from 32-bit to 64-bit?

Option 3: pg_upgrade

Is this an option?  Remember, I'm going from 8.4 32-bit to 8.4 64-bit.

Option 4: PITR

I believe this is not a possibility because of the bit-ness change but I'm listing anyways in case I'm mistaken.

Did I miss anything?

TIA,

Greg