CW is probably about 50% D/C, higher than SSB but obviously a lot lower than RTTY, AM or FM. To make an amp "sellable" it might have to be marketed as SSB-CW only, or verified to work at 100% D/C, or be derated for full D/C operation as many are. Hams are somewhat used to 8877 amps which can run 100% D/C at legal limit power with enough air, and will be operating well within their limits at that power. But SS amps are a bit different. TEC cooling is interesting. We use ordinary water cooling of our CPUs in HPCs here, and that works darned well and should be a strong consideration for those who like efficient cooling systems that don't make a lot of noise. Freescale says "Tj 150C" (although FETs have no junctions, but we know what they mean) and derates MTTF very quickly above that...down to about zero if you go much above that.