I bought some heatsinks with adhesive from ebay.
I don't know how well they perform. Checking the temps while printing is still on my ToDo-list ;)
But I've built an almost airtight enclosure for the printer and did some prints with Polymaker PC-Max (Nozzle 260°C, Bed 110°C, Inside the enclosure ~40°C, print times 3-5 hours) and everything survived ;D
Oh and I replaced all fans with more silent ones (same size though).
Except for the drivers, caps and resistors I haven't made any changes to the board.
I did experience occasional 1mm layer shifts in the X-Axis. But I think those happened because I also switched from linear bearings to igus bushings. I stepped down printing and travel speed from 3600 to 2400 mm/min and everything printed fine again.
Also on my ToDo-list: switching back to linear bearings on the X-Axis :]