If you get frustrated with Firecell, keep in AI4 till you get 9K and make Limitless Speed
First off I love your guide, find it really useful. I'm still grinding towards a fully upped arena grinder. Had some go at it with the halfblood grabow (pretty good against bronze), but need something more consistent
What I wanted to say that I really really hate limitless speed
I find it very inconsistent and much less practical than firecell. I'm running firecell with 4 upped hourglasses (and upped fractal because I got that from a spin) and against the winnable FG's it has a great win percentage. Limitless speed on the other end is very dodgy especially because it's an 8 card combo. I usually end up having my hand full, so I can't draw and more often than I care to admit I end up with all 8 cards in my hand without having the mana to play them all. Also like you write in suggestions, you prefer the slim version, but thats murdered by any poison, momentum and decay. The fatter versions are a bit unbalanced on the other hand, again being unable to draw due to the heavy number of cards you need to keep in hand.
Just saying
So for any newbies like me, keep using firecell and skip limitless speed if you get fustrated. Just up the hourglasses.