IMO they’re not too lardy/overkill for XC trail riding – esp if you do plenty of stuff in rocky terrain, or get a bit aggressive with the bike. I’ve switched over to Flow rims from DT4.2’s to get a bit more stability when running low pressure with fatter tyres. Have experimented with various pressures and they’re superb – with high(ish) pressures and fast tyres they’re absolutely awesome on flowy trail centre type singletrack, so stiff for quick changes in direction. Don’t really notice the additional weight of the rim over 4.2’s either. Go for them – I don’t think you’ll be disappointed.