I think you are on the right track and would go with the larger pump and hose and run it to your drain... Seems like the easiest way with less steps...
This is coming from a guy who does near daily 100% water changes with buckets still... granted it's only a 55 gallon but still a PIA... The way my office is set up it is far too winding and far to run a hose and when I used to dump it outside it was killing the grass... So I get my bicep workout in and haul the buckets. I am pretty efficient with bit but wouldn't recommend it.
I would grab that pump or the biggest one you could afford and fire that water away...
Oh and office tanks rock!!! Good luck and share some pics and enjoy it!!!