I've used Parcel2Go a lot over the last year and found their service to be excellent, although I know other people have posted about less positive experiences with them on here.
The service gives you access to B2B couriers that you would normally need a corporate account for, so you can use UPS, DHL (now called Yodel) etc.
To be honest, I've never sent anything insured, it's always been just the regular service. I've sent a titanium frame, several pairs of forks and other high value items.
I would personally not worry too much about the insurance and spend more time getting it properly packaged.
In particular, you must put a bracing strut between the rear dropouts; an old axle and QR usually do the trick but if you've just got a new frame, you should find that it came with a plastic brace itself. Bubble wrap to Nth degree and seal up the box well. UPS is pretty trustworthy and shouldn't cause you any worries with it not being insured.