Dare I say it...........
I work in insurance (abuse to follow no doubt) and was interested by all your comments.
The problem we all have is that nearly all of the cost of insurance is driven by factors which we have little control of:
1. Postcode
2. Age of drivers
3. Vehicle (not up for negotiation!

)
4. Occupation (often misunderstood - mostly it makes no difference, but if insurers don't like it - professional sports etc - you will be declined or hit very hard)
After this comes NCD (makes a huge difference - you should usually protect it if you can), weightings for convictions, storage, mileage, classes of use etc. Excess makes a difference too, but for a car like this a high compulsory will usually be in place.
Best thing to do is make sure that you receive as many quotations as possible. (I will not mention any specific companies)
I'd recommend that EVERY RENEWAL you checkout the optimal quotation via the following four channels:
1. An internet aggregator (some of you have mentioned examples)
2. A specialist broker (lots of ads for these in the motoring press)
3. A mainstream broker
4. Any affininty group memberships to which you may have access due to age(!), occupation, high net worth etc.
Why the broad range?
Because insurers are constantly battling for volume. You may receive quite different quotes/cover even from the same insurer if you try different distribution channels. They will often do preferential deals with some of the above distributors predicated on volume, commission rates, or access to a "preferred" client population (e.g affinty).You can also get freaky diifferences in rates, often simply because, for example a small difference in your age/postcode flips you into a better tier with one insurer compared to another.
Make sure that you do it every year. The UK market is massively competitive and moves fast (literally rates will change every day via some channels as they manage exposure, volume, market share etc). This might seem like a chore, but the beauty of phone/internet means that you should be able to investigate all channels within 1-2 hrs. You could easily save a three figure sum, so as a net hourly rate it isn't bad!
Remember, if you are luck enough to own 3 /4 + cars you may find it advantageous to insure them as a private "minifleet" via a specialist. Why? Because insurers know that you can't be driving more than one at a time....
If the quote is "branded" through a distributor, always ask who the insurer is and satisfy yourself that they are a company you want to deal with. They will (nearly always) be the ones who will handle/be responsible)for your claims.
Gap insurance has been mentioned. I'm not usually a massive fan of Gap and have never bought it before, but the Cayman:
1. Is scarce/new. Will be difficult for insurers to value accurately as few will be available outside Porsche network for a while (the benckmark they will use)in the event of a total loss. They may value low.
2. Residuals will be high
3. If like me you bought your car new with carefully considered options chances are that you will not want a used example from outside the OPC network.
So.......I'd buy it. But investigate (same channels) options. Porsche price looks high to me (many manufacturers' deals are). By the way, remember that nearly all insurers will replace your car during its first year
following registration , including options if you declared them, as standard within their policies. So Gap is only usually required after this period.
Check out your motor and Gap wordings carefully, and if you engage a broker make sure that they are good and then take their advice!
One more thing - don't crash!
Good luck.