Plain or coated, sizes and number of flutes?

I'd just use them as fast as you can and as you say keep them for difficult material. I rarely use them but if I have a hard spot in an iron casting may get them out. ER Collet works for me

I can't see your exact ref number but if you look at the pdf blue circle page 24 & 25 that shows a 3 flute 6.5 cutter on the right and on the left are feeds and speeds. At the start of the blue section that gives you what the 1a to 13b means – each colour is a material and the letters are different hardnesses of that material.

So taking the top purple for steel and 1a for the softest which would be free cutting MS that gives a speed of 140 m/min (don't think you have the Alpha) That means the edge of the tool needs to be moving at 140,000mm per min which on a 6.5mm dia come out at around 7000rpm. The other columns are how fast you should feed for different types of cut

With cutters of 6.5 you will be OK for speed. My Bridgeport varidrive rattles a bit above that speed so it is a self imposed limit and I have no problems running carbide cutters. For ME work think of them more as posh ridged cutters for a nice finish rather than high metal removal rates.

Chris, have you ever investigated the cause of the rattle? Mine is becoming more pronounced within the last 12 months or so, and I'm wondering if I should be doing something about sooner, rather than later. I recall seeing a note a long time ago in one of the BP manuals about curing a rattle by readjusting the HI/LO gear lever stop, but I haven't investigated to see if it applies to my machine. Manually moving the lever a bit further past the detent doesn't seem to make any difference.

Roger

Bridgeport rattles seem to be spline chatter on the quill and also the varidrive pulley problems. Perhaps JS can help out here?