I've been reasearching this somewhat heavily. I got in contact with "WalterAtMarchPump" who has been extremely helpful
and also a brewer at the new Witch's Hat brewpub in Ann Arbor, MI.
Walter was kind enough to take time out of his day to test some things for me. He hooked up their "815-PL-C" to pump through about 5 feet of 1/2 ID hose, then into about 2 feet of 1" ID hose going straight up (a keg spear is about 2 feet and has an ID just under 1"). It was able to project liquid 2-3 inches upwards.
I wasn't sure if this was enough to get the liquid to run down the sides of a 1/6 bbl keg, so I also contacted a new local micro brewery in South Lyon, MI called "Witch's Hat Brewing Co.". I spoke with a guy (sorry, forgot your name!) who was very helpful. He said they will use a 1/25hp march pump to pump caustic solution, then water, then sanitizer through the sanke coupler/spear basically just as i describe. They do then open the kegs for inspection but he says its just a precaution, they have always been 100% clean.
So it seems one of these 1/25hp pumps should do the trick, and now i don't have to invest in 2 different pumps!
Thanks to everybody who provided feedback and suggestions here, once I get all the equipment together, i will post all the details of the setup and let you know how it went (it'll be a while).