I didn't have time to play much on the first day (Thu), but for Fri, Sat, Sun:
- I got my 5x on ~30 different tanks per day while running 100% XP boosters, so I made a huge amount of progress. Some of my better battles were well above 10k XP.
- I spent about 8 million credits on equipment, and maybe 3 million on consumables.
- I bought the following tanks: Nashorn, T-50, Lorr. 155 50, AMX AC 48. Basically, was only looking to buy Tier V, VI, VII, since those were the only tiers with the maximum discount, and that's all the tanks at those tiers that I had unlocked.
- Bought ~15 Garage Slots
- I didn't really focus on the Progetto Marathon, as I was just working on the 5x for my non-Elite tanks, but I still made a good amount of progress on it as I've completed 4 stages, and am maybe half way to completing the 5th.
My stats took a bit of a dip, but nothing too serious. 2239 WN8 & 57.84% Win Rate over the 4 days. That's entirely from me playing a bunch of tanks I'm not super familiar with that don't have all the top modules in a lot of cases, and has nothing to do with the 5x weekend; that nonsense is a myth
It was a great anniversary event. I almost don't like when they have sales and 5x at the same time, because the sale makes you want to grind credits, but the 5x makes you want to grind tanks. Yes, first world problems 
How much free XP? Hmm, wasn't really paying attention; always had a free XP booster going. Maybe 40k?
Now the plan is to grind the M103 as part of the On-Track until I can unlock and buy the T110E5, then I'll switch over to some credit makers that I also earn a lot of XP in to wrap up the Marathon. On a related note, I also bought the T2 Medium (tier 2) from that line, just because I wanted to Ace it, and drag my win rate out of the 30's. Played 9 battles in it and Aced it 4 times. That thing is super OP with the 15 shell clip. I guess I should feel a bit guilty, but it's sold again now anyway. Forgive me 