Hi - I've just bought a Sonata & need to replace the kite sheets & get a new pair of ratchet blocks for them. The old sheets are 6mm but a crew member has complained that they're tough to hold in a breeze. Would 8mm be too heavy? Also, re blocks. I asked Harken what size & they said they'd previously specced 57mm for a Sonata. But then they said 75mm would be a sensible choice for improved holding. Happy to get the larger ones if necessary but it's an extra £30 so if it's not necessary I'll get the smaller size. Any suggestions/help very much appreciated!