Hey Ian,
Getting the Ali to cut like butter is a very very sweet spot between many many things.
I do not think the power or speed of your spindle is the issue... but assuming the 200 watter is one of the DC ER11 spindles, they have much larger run-out than the 3 phase versions. And I believe this is your main problem. Run-out is where the bit does not spin around the central axis. As a rough guide from Ebay... the DC spindles typically say 0.03mm run-out (probably best case - they are just a chuck whacked on a cheap DC or brushless motor) where as the better three phase spindles (4 bearing) say better than 0.005mm run-out.
This is very important..... particularly cutting with such a small bit. Practically, your little 0.8mm bit is banging against your ali from a distance of 0.03mm every revolution.... imagine.
But power wise (and speed wise) 200W is a lot of power for a 0.8mm bit. 20000RPM or even less that that is fine as long as the feed rate is appropriate.... more sweet spot parameters.
Now onto the bit.... can you provide more information? what type and where from?
The smallest end mill I use for cutting aluminum is 1mm.... but even that is small and breakage is common. I would only describe it as butter cutting over 2mm diameter. only then does the bit have enough strength. But note that my run-out is closer to the 0.005mm......
Other things that play a large role in the sweet spot is the grade of ali.... the soft stuff is no good. it sticks to the cutting edge of even the best bit, then things rapidly go bad. Most Ali I cut is anodized, and therefore for good for engraving and cutting.
Material hold down...... particularly with thin stock.... very important. as soon as your stock begins to chatter, the sweet spot is gone.
Lubrication is a hot topic of this thread, and this helps greatly... especially if the grade is not perfect for machining. A little WD40, CRC, IKEA oil, or the all of the things that have been talked about earlier in the thread are good (i have no experience with the wax sticks but im curious....) And some compressed air to blow swarf away helps too.
But.... all the lube in the world will not help if you have bad spindle run-out... and ill bet you a nice little selection of bits in the post if this does not turn out to be your main problem.
Cheers,
Tim