I have the JOM Bluelines on my Astra H Twintop and the ride isn't harsh at all. It's a lot less harsh than my old Vectra B that had Spax Springs and shocks.Don't go coil over you will hate the ride very hard not nice, get some good springs and shocks will be OK. I have pro sport springs and ta tec shocks.
I have 18" Penta's with 235/40/18R tyres on the Twintop and I fitted the coilovers at the lowest setting, then just wound them up the same each side to give a bit of clearance. I then took it to have a 4 wheel alignment and let them adjust it so the geometry was correct. The told me that I'd need camber bolts to go any lower than what they set it at, not sure how much lower than standard it is, the coil overs are wound quite high up and it's still pretty low.bornxenon, size of wheels are on your astra and what hight did you adjust your coil overs to?