For plains game in Africa I have used a .30-06, 8x68S, 9.3x74R and .375 H&H Magnum.

My first safari in Zimbabwe I took a .30-06 with 180 gr and 200 gr Nosler Partitions. I had some trouble with the batch of 180 gr Noslers I had with. So switched to 200 grs which I also had with. Most people do not report problems such as what I had therefore I assume it was a "bad batch". Took an eland, kudu, wildebeest, zebra, warthog, duiker, and impala.

Hunted Namibia with the 9.3 DR (286 gr Woodleigh PP) plus a borrowed 8x68S (220 gr A-Frame). Took 2x gemsbok, 2x springbok, 1x hartebeest, 7x warthog, +

Hunted South Africa and Zimbabwe was with a single rifle in .375 H&H. Other than buffalo took 2x bushbuck, 2x zebra, 2x impala, 1x waterbuck. 300 gr Woodleigh WC SN.

A .30-06 powered rifle is fine. A medium/big bore such as a .375 is un-necessary but also fine if you wish to take one. IMO the ideal is a 8x68S, .300 Magnum range for a dedicated plains game rifle with a 200gr premium SP projectile.