Gabriel (wa) is a great card against speed because you can knock out a few of their super can't be negated battlewinners, which will lengthen the game for you giving you the advantage. Speed is fast and potent, but small size (50 cards) means it usually won't be able to overcome losing it's battlewinning enhancements. Speed wants a short game, and if you can slow it down with many of the above mentioned counters, you will have the upper hand. Gabriel is also versatile against other deck types.
As was mentioned above, if you want to defeat speed, playtest it alot and figure it out so then you will better understand its weaknesses and then expolit them.
As far as the 16 card limit, I have not seen it really negatively impact the modern speed/aggro decks, but it does mess with the older original versions that used to draw the entire deck in a turn or 2. The limit also helps impact the massive card drawing that type 2 saw in clift/gabe's sin in the camp deck, where the card drawing would quickly setup the lockdown and game over.
High priest's plot can be alot of fun, too.