Yeah, the 7750 is considered the slowest according to:
I would say re-eBay it .... Or try posting in your local newsgroup (Perhaps ott.forsale.computing for Ottawa... tor.forsale for Toronto.... try http://groups.google.com
and finding a forsale newsgroup for your particular city.) This may mean a quicker local sale at a slightly higher price than eBay because the guy can drive to your house to look at your BlackBerry. This forum also has a "For Sale" forum where you can try to sell your BlackBerry first too as well, before buying a new BlackBerry!
(preferably from one of this site's sponsors, of course. <shameless plug>
Then, if you want the best, the current cream-of-the-crop BlackBerries are 7250, 7520, 7290 and 7100 (the Bluetoothed 32 megabyte models).