I was thinking of trying that myself as having player FF4 solo I think it's a tough one for the Germans.
Although you can still hurt other thanks with the standard AtB PzIV counter by getting into short or close range combat.
In general I think as long as you're willing to play a FF twice with both players getting chance to use the upgraded PzIV things should be OK.
Standard PzIV in CC is red 5FP+4/2 = 4. Upgraded is pure 5+4=9.
Short distance 4 and 8 respectively. I find the difference huge. I wonder how Germans would do in Bunker FF, where they had 3 and now would have 4 tanks with anti-tank capabilities (and PzIV is well-armoured).
Of course, given both players play as Germans, difference is balanced inter-games. Thank you both for this thought - somehow not came to my mind earlier.