If you can get away with the small cutting area of a mill type machine, I would personally preffer a mill over a gantry type machine for PCB and small Aluminium parts.

The reason being they tend to be more accurate and easier to maintain. Most mills are also built well ie Sieg x3 or Syil they have large companies behind them that make mills professionally to work in light industry, small gantry type routers sub £10,000 tend to be made of cheap materials by small start up companies that don't always have much experience in what they are doing, im thinking aluminium extrusion and plastic laser cut mounts and all the rest of it. I think some of the lower end gantry machines are being sold by people who view them as toys rather than working machines capable of producing parts. Which is a shame cause there is a big market out there for a good £5000-6000 quailty router. I do think the chinese however have actually made some of the best small routers in this price bracket.

Do you know what feedrates you generally use for PCB milling?