I played one game with classic rules, and I did enjoy it, but I prefer with overdrive.
As there is no overdrive I think games probably tend to be more equal. In general I'd say there is only 1 good early game strategy, as end game in classic you are always restricted to max 1 buy per turn, so early game players will quickly buy 2 or maybe 3 gains, combined with some moves to make sure they can buy a card each turn. After buying a 3rd gain the gains on the market (2 out of 6 cards) become completely useless.
Maybe move-rushing has some more potential in classic compared to overdrive games, as without overdrive it can be more difficult to defend.
For competitive play to me overdrive is clearly the way to go. If I would play this game IRL (I have finally ordered the game!) I can see myself playing classic rules unless the other player is an experienced boardgamer or chess player who can calculate moves well (including overdrive means much more options to calculate)