I’ve got a 24x12x1" block of 6061 aluminum for my next project, and figured I’d try out a rougher/chip-breaker style end mill to see if it’d help any, in terms of letting me be more aggressive. Ended up trying a few others, too, so I’ll share my subjective results and hopefully get some feedback from others.
All of the cutters were run at .1" DOC, .05" WOC, 169 IPM, 30k RPM, Fusion adaptive clearing entering from the side of the stock. All are .25" cut diameter, .25" shank.
Makita router w/ Elaire collet
Stickout: ~1.125", except for the Amana HSS1622, which was about 1.375".
Runout: I measured .0025" at 1.125" stickout
Upgrades: steel belts and HDZ
Lakeshore Carbide TAS rougher, 3FL, uncoated, .8" LOC: Visibly bounced along the surface with huge deflection when trying to enter the first adaptive cut and sounded awful. If this were one of my 1FL end mills, it would’ve snapped off right away, so these things seem pretty tough. Once I dropped it to 60% feed rate (101 IPM), it stopped deflecting so badly, but it still sounded terrible to the point that I didn’t want to leave it running.
MariTool rougher, 3FL, ZrN, .5" LOC, : very slightly better than the TAS, I could run it at 100% feed rate, but still not confidence inspiring to run a whole job this way.
Carbide3D 278-Z 1FL, ZrN, .75" LOC: sounded good and good finish at 110% feed (186 IPM). Still fine at machine max (196 IPM?), but starting to see some extra noise/chatter.
Amana 51402-Z 1FL, ZrN, .625" LOC: similar to the C3D above, very slightly worse chatter.
Onsrud 65-023 1FL, polished uncoated, .625" LOC: I had high expectations after using the 1/8" version of this on some copper and seeing how smooth and quiet it cut, but it had high chatter. I tried adjusting feed up and down a bit to see if it was resonating, but it exploded. 
Amana HSS1622 1FL, uncoated, HSS, .625" LOC: what a champ, considering the price - at 30% feed (51 IPM), it produced a decent finish. I was able to push it up to machine max (196 IPM) and even beyond (I adjusted my GRBL settings and saw as high as 315 IPM during cuts). It didn’t sound great at the high speed, and it was deflecting enough to leave .3mm gouges at the bottom, but that seems OK for my roughing needs. Afterwards, I did notice that the very tip of the flute chipped off, leaving me with a tiny chamfer on the tip… stronger than it started! (Or a per-job throw-away). Impressive, given the extra stickout due to overall length, too.
Any thoughts?
I was disappointed in the roughers. I guess my machine either is not rigid enough, or doesn’t have enough force, to push a 3FL end mill around? I also tried 20k RPM and .2" DOC, with even worse deflection. It all “checked out” in the (excellent) gmack spreadsheet, though I’m still learning what I can get away with.
The HSS end mill was a pleasant surprise. Carbide + ZrN looks like the better choice for finishing passes.