Hiya, I was reading all of your hesitation (and rightfully so) with moving your sites. Why not sign up with the new host and move one of your sites over and see how it goes. 2 months at ~$10 or so is a small price to pay for the peace of mind of knowing what it will be like once you move all your sites over. Of course if all of your sites use a common SQL backend or something then maybe this isn’t an option.
Moving one would allow to to test drive the new host and see how they are with backups/speed/reliability etc. In fact, I would pick your smallest site and then really test all the features you need by asking for a restore to see how long it takes, emailing support with some “urgent” question you need answered to see how long it takes to get a reply, how long it takes to get a tech who actually knows what they are doing on the phone if you have a problem etc.
Just consider you are doing a review on the host and approach it with the same detail. A phased approach rather than an all or nothing cutover is usually the best policy when you are dealing with revenue generating sites and new vendors of any type.
Hope this helps,
CBW