I just got my crusty basket case GS1150E running, and did a 530 conversion. I'm mostly commuting and highway riding, I'm not drag racing. I went way up to a 17/42 ratio. Runs 100 kph at just a hair over 3k RPM. So much torque, and 1st gear is so short that it doesn't even feel close to over-geared. I actually bought an 18t front as well to try. I got the parts info from Z1 but ordered from Fortnine as I'm in Canada so shipping from the US kills me and I avoid it when possible.
Z1's website gives part numbers and shows OEM fitment and also shows what else a part will fit. For example my front 17t sprocket is OEM fitment for a Hayabusa which I thought was cool.