Replace Heidenhein w/ EMC?

Have a good friend, an auto mechanic, that loves machining and I've been
helping him put together a machine shop for play mostly. (though we are
discussing some ideas for products and a mutual mfg venture)
When he wanted a CNC mill I suggested finding a dead Boss controled BP
and refitting with Ahha as about the cheapest and fastest way to go.
Then one of my customers decided to get rid of their CNC mill at a
giveaway price, $2800 with tool holders and CAM. I don't recall the
exact model control, but it's a Heidenhein control in a honkin' huge
box. Down the road he'd like to go to a PC based control, and I
mentioned just having recieved the BDI disk.
Would like to know if EMC is capable of giving roughly equal performance
in terms of speed and accuracy. Existing machine (Wells Index) uses
linear scales in addition to motor encoders, can EMC use these as well
or should they be offed with the Heidenhein control?
This is a no-hurry project, probably take the two of us a year to figure
out the interface issues... Just want to know if he's going to be able
to rapid and feed at roughly equal rates to what he has now, and if not,
how much will he have to give up?

Thanks,

Jon