I believe that 3456 and 5760 EME are worth pursing for several reasons:
1. Dish gain is high enough on a reasonable size dish(8 foot or larger)
2. At 3456 it is still possible to use a 7289/2C39 type tube for power
and on 5760 there are
a fair number of TWT's available that put
out 10 to 25 watts
3. There are great PHEMT's available that could with some work give
a 0.3 to 0.4 dB noise figure
4. With the lower dish gain it might be possible to avoid an expensive
dish positioner(at least initially)
5. Relay isolation and losses are managable