/* Why not try e.g. the 2.45 GHz found in almost every kitchen inside a micro-wave oven ? No idea if this frequency is better or worse than any other proposition. */
It depends on character of signal. Common induction heaters generate high enough portion of higher harmonics, despite they operate at 25 kHz frequency only. Rossi once noted, that the ECat doesn't start, until it's not powered with 220 V AC and thyristor/triak regulation is not used. So that even common AC current may work well for LENR, if it gets chopped fast enough.
The emission and catalysis of LENR by EM waves has most quantitative support in Frank Znidarsic theory of cold fusion, according to which both atom nuclei, both the orbitals behave like the elastic bodies across which longitudinal and transverse waves resonate mutually. Frank derived the characteristic frequency of this resonance at the case of so-called impedance matching: under such a condition the orbitals undulate heavily together with atom nuclei in standing waves, which would enable the merging of atom nuclei by selective resonance tunneling. I presume, multiple atom orbitals could undulate at the same moment being entangled - so that Znidarscic's predictions of resonance frequencies are substantially higher, than these experimentally observed - nevertheless the principle remains the same.
/* A microwave has already been shown to produce the LENR reaction in experiments by Egely. */
It hasn't - Egely just demonstrated the paramagnetism of pyrolitic graphite, which is rather commonly known stuff.