if you can afford panthers... you can afford a couple extra p4s to flank the enemy tank and keep control of the map earlier in the game. I dont believe in pretty much ever getting tier4 in a 1v1 unless you have complete map control from tier 1 and you want to troll them.
the real issue is probably that you didnt have good momentum before the kv8s come out. mines placed at chokepoints the entire game, p4s, a pak of your own and playing aggressively throughout the game is necessary.
if you wait until enemy heavies start coming out and looking for a counter, you are just delaying the inevitable. you have to build early momentum and use combined arms to stay competitive
I agree with the momentum part. But I'm going to say on a whim that having a well microed panther is a lot scarier than having 2 p4's. Yea, you can flank but a good opponent will lay mines and the potential for hitting them can be high (sorry I said button I forgot that this doctrine does NOT have guards), This being said, a p4 cannot take on either of these tanks head on, but the panther can do this all day. You have to be careful of course, he's not invincible.
I think the problem is people are "afraid" to go tier 4. So many people are in this "I need a panzer 4 NOW" mindset that you're actually putting yourself at a disadvantage. Your opponent will say "He will go tier 3 of course, everyone does" Just like you assume they will get snipers and su-85's. So... I usually have an "extended" (not sure what the norm is yet) tier 1 > tier 2. So 4 Grens, 1 MG. I then build a panzer grenadier squad and upgrade them with shreks and / or a pak if I really need to keep armor at bay. I then use the ostruppen doctrine to punish quick sniper kills from my enemy. Also, ostruppen may be helpful in battling the kv-8 as if he's melting your infantry you will start flooding the battlefield with cheap infantry and since they are cannon fodder you can use them to disable the kv-8 rather than your grens / panzer grens. If you then get out your tier 4, you have tons of expendable troops, and a panther which can RUSH ( if you feel frisky) the su-85 and kill it easily when the opportunity arises and it makes mincemeat of the kv-8, there is no competition between the panther and these two tanks. I say panther because it nullifies both tank pretty heavily.
Also, I edited the crap out my post, wrote it when I first woke up and it was full of mistakes, my bad.
Also, just for some math if you're interested:
So assuming you go Battle phase 1> 2> 3 like I propose to get you a panther, it will cost you total:
+ Tier 1 infantarie Kompanie: 80 mp / 10 fUEL
+ Battle phase 1: 200 MP /25 Fuel
+ Tier 2 Leichte Mechanized Kompanie: 120 Manpower / 15 Fuel
+ Battle phase 2: 200 MP / 35 Fuel
+ Battle phase 3: 200 MP / 50 Fuel
+ Tier 4 Heavy Panzer Korps: 160 Manpower / 30 Fuel
+Panther: 440 MP / 165 Fuel
-----Total-----
= 1400 Manpower
= 330 Fuel
Battle phase 1>2> 2 Panzer IV's
+ Tier 1 infantarie Kompanie: 80 mp / 10 fUEL
+ Battle phase 1: 200 MP /25 Fuel
+ Tier 2 Leichte Mechanized Kompanie: 120 Manpower / 15 Fuel
+ Battle phase 2: 200 MP / 35 Fuel
+ Tier 3 Support Armor Korps: 160 Manpower / 25 Fuel
+ (x2)Panzer IV: 640 MP / 230 Fuel
-----Total-----
= 1400 Manpower
= 340 Fuel
So believe it or not, the panzer Iv's actually cost a bit more fuel. Of course, the panther will hit a bit later than your first panzer IV, but take into account that your opponent may build an SU-85 regardless of seeing armor (which is very popular). On top of this, the ostruppen doctrine comes with a mortar halftrack (which may make this strat more expensive of course) but it can help to counter snipers and any AT gun creep. I've found these combined tactics wreck kv-8 play. Just my opinion.