What's the most you've increased your Steam level during one Steam sale?

It's pretty hard enough after level 50, when a single level 5 badge is not enough any more to level. I increased 11 at the last sale, and I only plan to go to level 80 now with crafted badges + whatever I get from sale badge. I have a gut feeling it will be worth to try to save more cards up for winter.

went from 48 to 77 and the sale hasn't even started yet

Guy in my friend list went from 185 to 339 yesterday. He had around 25-30k cards to craft.

I have 17 lvl. Is there any reason gain more? I heard that it makes higher chances for card packs, but i'm not sure if it's true.

PS. I also heard that at lvl 50 you can shoot fireballs.

I was Level 33 yesterday today 42

Well,during the 2013 winter sale i leveled up about 1-10 times,while in 2014 one i leveled up...7 times. Well,thanks to cards that was easy to sell for another pack of cards to craft. And yet,i ever level up(as i found out leveling outside of sales bad)when sales begin,even though this will cost me alot of money. Some people call this stupid,but as high level users found out they will never earn crafting/level rewards on events if they don't ever spend money. So the result is to earn good rewards you HAVE to pay for events.

I'll probably go from 31 to 40 soon™

I went from 10 to 20 when the mysterious cards popped. I am waiting for the sale to craft my other half of badges, or maybe just sell the cards, it will depend if there is an event or not.

I only ever levelled up, when there was some incentive, e.g. when I needed lvl 5 for the free holiday card from community choice, or when crafting the cheapest cs:go badge effectively resulted in more money than I spend on the cards (during sale, when selling background+holiday card+emoticon). I've made it to lvl 13 that way and I don't think I will go much higher from there.
I would probably craft a few more badges if backgrounds looked better in general, if cards for those games I really like were cheaper and if there was something else to gain outside sales besides the background and those stupid vouchers.

Last winter sale i crafted before the sale started and in between sales >.< , now i have gathered enough cards to get to level 52 or something. It's enough since anything higher doesn't do anything.