what time period is the most even for US vs USSR?

[Imp]

Agree with Andys comment a campaign works well & can continue a bit further as first Abrams is not that effective suffering from a common problem you will notice with the US.
If talking tanks US generaly has better Fire Control but a pea shooter for a gun so cant capitalise much of the time. One sides praying for a hit the other for it to penetrate & the US forgot to install Giros so attacking can be a problem. Good fun as a campaign as it swings back & forth.
If you keep going unless patch has changed you reach a point where both sides have trouble destroying the others tanks as armour outraces firepower for a while.