Are there still programmable clock synthesizers with single ended TTL output leves (in 2019)?
You can easily find &quot;any&quot; logic level VCO that operates from 5 to 50MHz and then you can control it with a tiny trimpot to find the max rate at some Vcc voltage or CPU temp and decide what is optimum by cooling, adjust Vcc or VCO clock or make one.
NC7SZ14




simulate this circuit &ndash; Schematic created using CircuitLab
5~50 MHz 1.5 to 5.5V  Astable Multivibrator using Schmitt trigger Inverter
The clock f depends on RC values not the supply voltage as the ratios are fairly stable from 1/3 to 2/3 of Vcc. So 5V is no problem.  Buffer current needed = TBD.  This one is 32 mA.