The more resistance to the powder burn (tighter combination), the better it burns and produces more pressure, increasing the vel. per grain burned.
1,800fps is not high, for a small calibre rifle.
I would suggest that anything approaching 2,000fps+ is a good vel. for a slippery lube. My rifle had a 48" rate of twist and shot best at 2,240fps, however, that was with LHV lube, a VERY slippery one.
With a water based lube, around 1,800 to 1,850fps was best.