As for Grabbows, I've ran quite a few upped variants, and they benefits the most from the aforementioned speed increase of course.
All you need to go is observe each upgrade if you're sticking with this deck, which you can do in the upgrade screen (without actually upgrading). I'll list 'em for ya.
Graboid -> Elite Graboid: +2 attack
Phase Spider -> Phase Recluse: +3 attack, +1 cost
Sapphire Charger -> Elite Charger: +3 attack (best upgrade)
Flesh Spider -> Flesh Recluse: +3 attack (strictly better than Elite Mummy)
Forest Spirit -> Forest Spectre: +1 attack, +2 HP, +1 cost (very useful since Forest Spirit is so initially weak to CC, but means you might not wanna pack more than 2 Spectres)
Lava Golem -> Lava Destroyer: +2 attack
Pegasus -> Elite Pegasus: +1 attack, +2 HP (means +2 attack when diving)
Lycanthrope -> Werewolf: -1
cost (useless for you in this deck)
Dagger -> Dirk: +2 attack
Nova -> Supernova: x2 quanta, +2
cost (doesn't work in a Grabbow as you'll want Entropy mark to be sure you get
early, but since you run so many QP's, you could get away with as many as 2 Supernovas)
Quantum Pillar -> Quantum Tower: +3 random quanta when played (adds more speed than you might think)
There are several immediate optimizations you can do to make this a pure Grabbow rush. Here's an example:
http://elementscommunity.org/forum/rainbow-decks/hurrybow/Note that I'm using Arsenic for a weapon as it climbs in damage very fast and enables a soft way around shields. If you don't have one, you still have several better options than Dirk, such as Longsword or Gavel.