I think it is a simple matter of physics, Ian. An eight foot purpose designed rod will cast better than a seven foot multi-purpose blank. You will of course often have times when GTs are milling around the back of your boat but GT popping is a sport of just repetitive casting and the longer and more often you have that popper in the water, the more fish you will catch. It is not a coincidence that the longest and best casters generally catch the most fish.
I don't think it would be a stretch to say I am a highly competent caster but the one angler who I fish with from time to time who has me covered easily is Damon Olsen from Nomad Sportfishing. Damon would be one of the best casters in the sport and he will outfish me easily four out of five days for the simple reason that he is a superior caster. On that one day, I will get lucky!
but I think that superior casters make their own luck in this sport.
i suppose you could try to back your boat in to cater for the lack of distance but that isn't always feasible casting into some areas.
It's hard to say what distance you need. In the Maldives, try 100m but in some other places I've fished, you may only need a 50-60m cast. there will be areas you can't get your boat into where you need to hit a small spot that is 90m away. You will find that hard work with a seven foot Calstar.
The other thing is that the Calstar blank is a blank that is being adapated to use for popping. The specialised GT popping rods have been designed specifically for casting and popping. Most people who start with Calstars end up moving to the more specialsied rods in time.
That said, it would also be fair to say that the Calstars have proven themselves to be capable popping rods.