No, you dont. Process I sent you, the solution Heiko Ankerbrand gave works 100% for different hardware, specially if you wish to keep same IP addresses. Actually, even if they are different, it would still work, as long as they match on OS level and in topology.
I did that 7 times so far, 6 times IPs were same, 7th were little different and worked every time and EVERY time, hardware was totally different...couple times from 4000 to 6000 series and last few times from 5000 to 9000 series, so that absolutely would tell you that different hardware works, as long as you ensure the other things I mentioned are right.
You can replace the cluster if you want and do it "clean" way, but it will take you very long time. Btw, I never had any complaints from customers after doing that process below.
https://community.checkpoint.com/t5/Security-Gateways/Replace-Upgrade-Cluster/m-p/157228#M27268
Andy