New poster but long time lurker.

I have he need to cut a number of long, deep (up to 25mm) slots in 6082.
Current strategy is to peck drill a number of 6.5mm holes to depth and the run the slot with a 2 flute carbide end mill at 80% F and S (12000rpm, 1200 mm/min).

This does work but it generates a lot of swarf and the chips fall into the holes.
The question is, would it be better to use a smaller cutter. 5 or even 4mm? Is slot depth a factor?

The machine is a steel frame gantry with flood cooling, 2.2kw spindle.