I have been playing it on PS4 since January. It took over from BF4 and I haven't played much else since. I haven't spend anything on it so far, which I find a weird sort of satisfaction in. In tier 8 I can earn a little silver but tier 9 with my stock E75 have been a silver pit so far. Like you I kinda loose interest around tier 7 since the grinds get so long. Premium would help with that but 6 months would be the same as getting BF1 new so I find it a little too hard to justify since I could loose interest at some point.
So far the highest tier tanks I have in each line are:
E75 (tier 9 heavy) - Not enjoyable so far. It meets too many Tier X TD's that will eat you raw for the slightest mistake. Top gun and turret will eventually help though.
T29 (tier 7 heavy) - A little too slow to be fun but a monster hull down.
SU-152 (tier 7 TD) - The crazy alpha damage makes it fun to play on occasion.
Churchill VII (tier 6 heavy) - Glacially slow, but tier 8-10 in that line looks fun.
Type 4 Chi-To (tier 6 medium) - Not that good but tier 8 and 10 looks like I would enjoy them.
T-34-85 (tier 6 medium) - The regular T34 was awesome. T54 and on should be good as well.
KV-85 (tier 6 heavy) - Lousy gun depression, and not that fun, but next level and on should redeem that.
M44 (tier 6 arty) - When you just want to relax.
StuG III Ausf. G (tier 5 TD) - Sold it and haven't picked it up again.
FCM 36 (tier 4 light) - Haven't played light tanks much so I'm working towards the ELC to properly try it out.
I have an average WN8 of about 1450 over 2030 battles so average/good as well. On occasion I can have a 2500+ session but atleast an equal ammount of 1000 WN8 nights where everything just goes wrong.