4000 SFPM is about the bottom of the speed range for abrasive metal removal, and 8000 is the upper end. A machine with a VFD control allows you to select the best speed for the job.
so I should look for a belt grinder with a high belt speed around 5000 and up correct?
I cannot ever remember seeing a machine like you describe for under $1300-$1400. You'll want a minimum 2HP motor (for an 1 1/2" or 2" belt), and 3-5HP for a 6" belt.
I'd rather just buy a big heavy duty one the first time rather then buying a cheapy and have it crap out on me.
The 20" disc sander from HF is waaay underpowered. My Delta 12" disc is driven by a 3HP motor (with VFD speed control) - 3HP is none too much for a 12" disc. The HF machine needs a minimum 6HP to be useable.
As Planet X said, a contact wheel is essential. Of all the machines mentioned, only Burr King & KMG have contact wheels. Probably 85%-90% of the grinding on my Burr King is contact wheel, with the balance slack-belt or platen backed.
HTP Invertig 201
Trailblazer 302, Spoolmatic 30A, Suitcase 12RC