Seeking sweet spot in cloud hosting

Well, I am looking for a cloud hosting company for my complex web site. I am not that experienced with servers beyond using Cpanel, etc. I am currently using Hostcolor for my shared hosting and they have been fine, I just do not know if they offer that great a cloud solution, partly due to their smaller size as a company.

As a result, I began to look at Rackspace, Liquidweb, Logicworks, Firehost, Hostway, Amazon's solution, etc. and the more I dig the more confusing it seems as to what they offer and what I would need ...

My priority is that I want fast page serving, and the ability to handle big traffic bursts nimbly. I intend to ramp up this site massively in the next six months with massive marketing and PR pushes and I do not want to get into the position where the site begins to look amateur due to slow loading.

My problem is that my web site has some very heavy php code that resulted in upwards of 15 second page loads (for a few of the key pages) on shared hosting. I do intend to at some point get a copy of the site onto a server with root access, maybe on my own laptop, so I can run some diagnostics to figure out where the slowdown is. I am guessing, based on other people's discussions on these boards, that the slow performance is due to the way Drupal loads each module individually (and I do have a LOT of modules, alas).

I do think I will need managed hosting in the sense that I do not want to have to learn how to run a server, the site will keep me busy enough managing visitors, maintaining the site data itself etc. Nor do I want to be in a position to have to respond any time of day or night on a moment's notice when the server has a problem.

Finally, I would prefer no contract if possible, in case the site does not take off, though this is not as much a priority, since I think the site WILL eventually find its audience.

Having said all this, I imagine there is a 'sweet spot' - some cloud hosting provider that is kicking hind quarters compared to the others, is relatively large and established, and provides prompt 'above and beyond' service, and that is also relatively AFFORDABLE for what they provide. A sure bet, basically. Then again, maybe there is no such 'sweet spot' provider.

If the site really takes off, as hoped, I will probably end up giving the hosting company quite a bit of business - the site is a next gen reinvention going up against some very successful web stalwarts - even if the site hosting might eventually be switched from cloud to dedicated servers.

Any suggestions would be of great value. I need to switch over in the next few weeks if possible since my current shared hosting contract runs out in early June and I would like to switch while the existing contract is still in effect, as I am also running another smaller site and also as I am not yet experienced in moving Drupal sites to new hosts.

Thanks,
Rob