slow initial access to wordpress

Hi,

We very recently moved our site which is partially wordpress, to a new web host. Web host has very good reputation and no complaints about their service so far.
At the same as moving host I upgraded wordpress to 3.5.1

Problem I have is that first access to wordpress section of site can be very slow, 8 to 15 seconds. The rest of site works fine with good response times. After that first access the same page will reload quickly even after clearing local cache.

So it looks to me that either it is MySQL server cacheing being slow at host or possibly wordpress doing some kind of initialisation which looks like it only happens once a day for any user.
I have the cron in wordpress disabled and I can’t see anything in logs which is running any cron when this happens.
WP only has 75 posts in it and db has been exported, tables dropped and then imported so db should be highly optimised.

So question only remains, is there anything in 3.5.1 which could cause slow initial load just once a day for any single IP?

Or do you think it is MySQL server being slow?

thanks