Maximum continuous plate voltage for the GI-7B (and GI-7BT which has a more robust node) is 2500 volts, although the tube was designed for pulsed microwave operation at up to 9KV.http://www.radars.me.uk/gi7bt.htm
The GI-46B is basically a GI-7B with a more robust grid (20 watts grid dissipation instead of 7 watts).
For linear operation, maximum plate voltage is usually set round 2300-2600 volts, although some designs use up to 3000 volts. More conservative designs set the plate voltage around 2000 volts. At around 2400 volts you will need a fairly high bias voltage (around 30 volts) to keep the standing current within limits of 100-120mA.
In practice, these tubes should be carefully gettered over an extended period before use to improve the vacuum and reduce the risk of arcing. A ood control board is also essential.