Common values are:
6L6/KT66/6550/KT88/KT90 - 4K/tube nominal for Fender (though the 3x10 bandmaster ran 2.67K), 3.6K to 4.2K are typical, sometimes as low as 2.5K, maybe up to 5K+ for an amp that has a compromise primary Z & can run 6V6 as well. Some old PA amps ran 7.5K. I'd normally go with the Fender value as this gives some leeway with ext cab jacks. Halve the speaker load with a 2.5K primary and you can wave goodbye to your power tubes!
EL34 - typically a shade lower than 6L6 (3.5K to 3.6K) but to all intents and purposes interchangeable with 6L6.
6V6/EL84 - Centre value might be considered around 8K/tube, some old PA amps ran 4.7K, early low voltage SE amps might be as low as 5K-5.5K, BF Deluxe is around 6.6K, up to 8.5K at the higher end for Princeton/Tweed Deluxe.
In short, stick to 3.6-4.2K for the bigger tubes & 6.6-8.5K for the smaller tubes if you intend to wire the amp Fender style, with parallel ext. jack, fed by the same OT secondary - an amp set up like this will normaly tolerate halving or doubling of the matched speaker load. If you swing to more extreme hi/lo primary Z, make sure you use a multitap OT & always match speaker loads.